Link 1-Colour 70
I go where the logical development
of the colours that I see in Nature (Cezanne)
BCM = Black Cell Matter
BSM = Black Synthetic Matter
MALDI = Matrix Assisted Laser Desorption Ionization
Shells , Pearls.
Interest in colour is part of the nature of man. Pliny thought that atoms were coloured. Leonardo Da Vinci asked why the sky is blue. Lord Rayleigh was struck by the colours of the flowers. Chevreul loved the harmony and composition of colours. Shakespeare used coloured images in his powerful poetry. Boyle had the intuition that colour was a sensation provoked by light. Padre Grimaldi was convinced that colour depended on radiation. Young gave great importance to the colours red, yellow and blue. Newton wanted to understand how to generate the colours. Goethe was fascinated by shades of colour. Dalton was actively surprised when he noted that his perception of some colours was different to that of his friends. Helmholtz saw the colours as a function of wavelength. Armstrong was immediately attracted by coloured reflections of some lunar rocks. It is now known that the colour one sees depends on the relative activation of three classes of visual pigments, or light-absorbing proteins, in the retine. The cone-shaped cells housing the pigments translate the absorbed light into electrical signals and trasmit them to the brain for interpretation.....
Colours come from light. A ray of light which passes through a triangular glass prism decomposes into various colours. In the rainbow small droplets of water provoke the same effect as the prism. Radiation or rays of low wavelength (475 mm) produce the sensation of the colour violet, those of a high wavelength (645 mm) that of the colour red, while the intermediate wavelengths produce green, blue, orange and yellow. The interval of these radiations, with wavelengths between 400 mm and 750 mm, is commonly called the visible spectrum. It is difficult to say what sensations are produced by radiation which is outside this interval, that is radiation in the so-called ultraviolet and infrared zones. The colours and shades of colour in animals are due to phenomena of selective absorption of light through the action of chemical compounds (pigments) or to physical phenomena or to both types together. The pigments are also called biochromes and the "physical" colours schemochromes (1). It is easy to distinguish between a biochrome and a schemochrome: the former can be isolated by chemical means, the latter cannot. Melanins and porphyrins seem to belong to a new pigments class : the electrochromes ( 21-23)
Biochromes or pigments
The blue of human eyes
Some chemical compounds absorb a part of the radiation which makes up white incident light, while they let the other part pass and reach the eye of the observer. Therefore the colours and the various colourations appear as the complementary colours of these which are absorbed.
Two different types of photon or radiation can reach the human eye: those not absorbed by the molecule and those emitted by the molecule which are rarer. From the moment that the photons hit the human retina with varying energetic content colour becomes a biochemical process.
The unsaturated composites are, in a special way, sensible to light. When there are no longer double bonds in a molecule and when these are conjugated the molecule is coloured.
The chromophores of animal pigments can be part of molecules, including complex molecules, in which particular structures which notably influence the colour of the substance can be present.
All the animal pigments, can be isolated and may often be obtained in a crystalline form. Naturally at an equal concentration and equal physical state there is no difference between the colour of the isolated pigments and those seen in animal. Being able to study the pigment outside the biological source is a great advantage for establishing the formulae of their structures. More difficulty is the study of the new class of pigments, called electrochromes like melanins and parphyrins (22) (23).
As will appear clear below, to our great surprise the variety of colours in the animal world correspond to only a rather restricted number of fundamental chemical architectures.
Schemochromes or pigments which do not exist
Several colourations of the animals are due to phenomena of scattering, interference and diffusion of light. The physical phenomenon which nature creates with an incredible perfection can be caused by a variety of optical objects: particles, microscopic prisms, lattices, stripes, thin strata or cavities. In general blue and green are schemochromes.
One of the most beautiful colours of physical origin which is seen in the animal kingdom is blue. The manifestation comes about because of particles, honey-comb cells or other optical heterogeneities, with particle diameters of ( ~0.6m), the same order as that of the wavelength of blue light, when their refractive index is different to that of the medium which surrounds them. This type of blue is only seen by reflection while with transmitted light reddish, brown or grey colourations appear. The relative size of the particles determines the intensity and the shade of the blue: the blue of the sky, due to the diffusion of solar light by gaseous molecules in the air increases in industrial areas because of the presence of very fine particles, while larger particles make the blue paler. After a storm the sky is bluer because the rain makes a selection of the particles and eliminates the larger ones. The blue of human eyes, the blue of the plumage of birds, of some reptiles, of the fish Hypsurus caryi and Trachinotus Kennedyi and the blue rings near the eye of the octopus Octopus bimaculatus are all due to a physical phenomenon which is commonly called Tyndall scattering. This type of colour, which is not modified by the angle of vision, unlike colours due to diffraction and interference, is due to particles or cavities of about 0.6 m in diameter, laid as a black or brown substrate, which are almost always made of melanin. Without melanin the blue disappears or reduces greatly: by absorbing the light reflected from other bodies the melanin prevents this light from masking the small fraction of light scattered by the particles or cavities.
It is easy to understand that the colour cannot be due to a pigment after considering some simple experiments on blue coloured biological material. If, for example, one takes a blue feather of a bird, first of all one notices that several different liquid solvents do not take on colours after the feather has been treated with them, that is one cannot extract the pigment, but if the feather is emerged in a liquid (e.g. carbon disulphide) and it is left for several days this slowly penetrates the spaces pushing out the air, and gradually, as time passes, a brown or black colouration appears because the liquid has a different refractive index to the air which it has replaced. If the liquid is allowed to evaporate the feather returns to its original blue colour. A different experiment consists of finely grinding the feather in a mortar so as to destroy the cellular architecture which produces the blue colour, which in fact disappears and is replaced by a grey or brownish colour.We can also easily distinguish a biochrome from a schemochrome in this way.
How the blue,green, yellow may be formed ( see Link 9 )
The numerous green colours in animals have a singular origin. Green is produced with a blue schemochrome added to a yellow biochrome which acts as a filter. Many examples are found among Birds, Reptiles, Amphibians, and more rarely among mammals. In man green is only seen in the eyes which, perhaps because of the infrequent cases of the phenomenon, are considered of rare beauty. The yellow biochrome is generally soluble in organic solvents and for this reason can be extracted: this interesting experiment can change a green animal colour into blue. In nature this occasionally happens by mutation: the frog can appear blue because of a genetic alteration at the level of the chromosomic DNA, and the loss of the capacity of synthesising the yellow pigment which filters the light.
White has a different origin. Surfaces and colloidal phases constituted by materials which do not absorb visible light, and which have subdivision states that do not interfere with the wavelengths of visible light, reflect white light without altering it and for this reason appear white.
Tissues of keratin interspersed with air spaces are responsible for the white colour of hair, like that of the fur of the polar bear, and of feathers. White can also come from the deposition of inorganic compounds in the tissues, like the calcium carbonate in Molluscs and Crustaceans, or from organic compounds like guanine and uric acid in the ventral part of Fish and in many Invertebrates.
Iridescence is a common phenomenon among Insects, especially among Butterflies and Beetles, but there is no lack of examples among Crustaceans, Cephalopods and Birds. Various types of Beetle (e.g. Cockroaches) of so-called metallic colours are strongly iridescent. The colour of the butterfly Urania riphoesus of Madagascar is not only due to the biochromes but also to particular laminae of small transparent scales which produce blue and green colourations. The iridescent parts have different architectures depending on the animal, but, in common, they all have the disposition in very thin interspersed laminae of air or films of material with different refractive indexes.
A dark stratum which is often constituted by melanin, as in the Tyndall effect, protects the purity of the colours from interference, in animals, since it absorbs the white or coloured background light.
The laminae which produce iridescence can be of chitinous material as in Crustaceans, Insects and Worms, of keratinous and proteic material as in the feathers of Birds, in the scales of Fish and of Reptiles. In certain cases crystals of chemical compounds can also produce iridescence, as in the skin of the squid where the effect is given by small ordered crystals of guanine in cells called iridocytes.
A good example of iridescence is observed in the copepod (crustacean) Saffirina at the Zoological Station of Naples: placed on a dark background it appears with a shiny copper and gold colour with red and blue shadows, changing ones angle of vision one may see blue, viola, red, orange and yellow. This effect, which disappears after the death of the animal, is due to submicroscopic laminae containing crystals of guanine which are found on the epidermal cells. It is interesting to observe that the female is not iridescent. This may be partly due to a different structure of the laminae and partly to the absence of guanine. Other examples of iridescence, even though less conspicuous, are seen in the hair of the golden mole Chrysocloris and in the feathers of the starling and of the turkey.
In the barbs (feathers) of the humming bird, and more precisely in the part where there is, an iridescent zone, one finds very regular granules of melanin deposited in mosaic form in a single layer surrounded by keratin. Since the melanin granules have a much higher refractive index than the keratin the phenomenon of iridescence is possible.
The melanin granules in the sack of the squid, which are round and very regular, produce the interference colours when they are dried with care. The iridescence can be explained, in that the granules become covered by a film of a mucilaginous material which is normally found in the sack.
Iridescence due to the diffraction of light is rarely seen. The phenomenon is produced by the most varied lattices of geometric forms. In the pearl the crystals of calcium carbonate deposited in grates decompose the light into characteristic red and blue tones. A case of iridescence by diffraction is that of the Aphrodite aculeata, a small marine worm which lives on theTyrrenean sea bed and has shining and iridescent bristles, where instead of a lattice the function is carried out by small longitudinal fibres. Other cases are seen in the Ctenophores belonging to the animals of plankton, and perhaps, the iridescence of the eyes of Ungulates (hoofed animals) is due to diffraction phenomena as well as to the phenomenon of interference.
Yellow Orange Red
carotenoids carotenoids carotenoids
pterins pterins pterins
flavines ommochromes ommochromes
Green Blue Violet
schemochrome + pigment yellow schemocrhomes carotenoprotein
bile pigments carotenoprotein ommochromes
carotenoprotein bile pigment echinocromes
Red - Brown Brown Black
pheomelanin pheomelanin melanin
(mixture of white and black) (light reflection)
Schemochromes are also keep their lively colours after the death of the animal. The thin iridescent laminae of the scarabs are so well made and resistant that the ancient Egyptians used them to adorn their tombs, and even today they are a precious ornament in some tribes in Africa. It is surprising that, unlike the pigments, the wonderful colours of a physical origin have not found any practical use. Timid attempts are found in some cloth, obtained by weaving threads of different colours or adorning the clothes with specks of glass or other reflecting material. With the use of different coloured plastic materials and the inclusion of sand one can obtain sheets and walls which produce different effects according to whether one sees reflected or transmitted light, as happens for the colours produced by the animal schemochromes.
Faithful reproduction of the complicated architectures which produce the physical colours in animals certainly presents a not indifferent economic problem, but their use would bring the pulse of a new multicoloured world to the palette of the painter and would give painting a new expressive force.
From our observation post, situated at the end of 1975, we can note that our knowledge about the colours of animals is more than satisfactory from the chemical and physical aspect. It is possible to compose, for example, a table which illustrates the relationships between the colours and the chemical compounds and physical entities which generate them and which allows us to make a first gross recognition of the world of animal colours. Some themes dealt with later in this work are the questions: What are the chemical structures? How are pigments distributed in animals?
Biochemistry and coloured vision
Optical physics, protons and electrons are the protagonists of what we define the first act of coloured vision. The second act starts when the photon reaches the retina. The latter has a system of receptors (rods), which serve to perceive small quantities of light, and a second system (cones) which serve to receive a greater quantity of light and signals. That is, the rods serve crepuscular vision (vision at twilight-vision in dim light) (scotopic) and the cones diurnal (daylight vision) vision (photomic). In the retina of the human eye there are about 100 million rods and 5 million cones; they are provided with small sacks containing pigments.
These have a high molecular weight and are generally formed by two easily separable parts of different chemical natures, one is coloured, and the other uncoloured and of a proteic nature which constitutes the main part of the entire molecule. The human pigments, called rodopsines, are formed by opsines (proteic part) and by 11-cis-retinals (coloured part).
In man there are four types of pigments, one in the rods and three in the cones; the coloured part, chromophore, is always the same while the type of opsin varies.
The pigments which are found in the cones vary in their maximum absorptions which are of 450, 525, 555 mm, that is, in the regions of blue, green and yellow in the visible spectrum. Therefore there are three types of cone with three different sensitivities.
The cis-retinal is very similar to vitamin A, in that there is an aldehyde group -CHO in the place of the primary alcoholic group -CH2OH that this possesses. It is immediately clear that this dietary vitamin is important for our vision processes.
One of the oldest recorded human illnesses, insensibility of the eye to crepuscular light, illustrates the action of vitamin A. When the pigment is hit by the light it splits into opsine and retinal and the latter successively passes to vitamin A. These chemical reactions can follow easily, in that they have changes of colour from red to yellow and to white, colours which correspond respectively to rodopsine, to retinal and to vitamin A.
A deficiency in vitamin A, which generally accumulates in the liver, impedes the synthesis of the pigments of vision and, as a consequence, produces blindness when the illumination is low. The administration of vitamin A prevents and cures the illness. (2).
Opsine is a lipoprotein which means that it is rich in lipids or fats, and it belongs to a class of compounds which are found, or even constitute many biological membranes. Cis-retinal and opsin are linked to each other by the aldehyde group and a -NH2 amino base group which is free of the protein and able to form a bond which is typical of the Schiff bases. The compounds, studied a long time ago by the chemist Hugo Schiff, are characterised by the -CH=N- group and are easily hydrolizable, that is one may add a water molecule and restore the starting product; this link is sometimes so weak that solutions have the equilibrium -CHO+NH2= -CH=N + H2O.
When the pigment is hit by radiation the cis-retinal (also called retinaldehyde) transforms into trans-retinal; this change of form of the molecule in space, which includes an internal rotation of the molecule, sets off a series of reactions, some of which, since they occur in less than a millionth of a second, can only be followed using flashes of light and very low temperatures. The main reactions are: the change in the form of opsine, the detachment of the trans-retinal from the protein, the reduction of the -CHO group into a -CH2OH group, the reoxidation of the primary alcohol groups with the formation of cis-retinal and its recombination with the protein. The very fast transformation of cis-retinal into trans-retinal is stupefying. Above all the first thing to note is that of the five possible cis isomers which the retinal can give the 11-cis-retinal possesses the lowest steric hindrance. However, the fact remains that to make the 11-cis-retinal molecule pass from the cis form to the trans form a notable amount of energy, about 25 kcal/mole, is required. To understand how this barrier can be overcome one must admit that under the action of light the retinal passes to an excited state through which the cis-trans passage is easy and that the retinal-opsin link favours this passage. This molecular mechanism is, besides, common throughout the animal kingdom.
Naturally these mechanisms contribute to understanding only one aspect of coloured vision, that is, how the photoreceptor pigments manage to discriminate the various wavelengths of light, but they do not explain how the information is transmitted to the brain and how the brain deciphers the information received.
In the light of these recent discoveries, the colour blindness which some people suffer can be explained by the lack or the alteration of one of the rodopsines of the cones. Successive studies will allow us to establish the number of animals which are permitted coloured vision, a number which, taking into account some recent results, will be much higher than biologists have suspected to date. As soon as rapid analytic techniques to differentiate between the various rodopsines are developed we will be able to check which animals have the capacity for trichromatic vision. Such vision, though, may differ from ours, both because of the different positions of maximum absorption of the pigments and because of a different elaboration in the brain of the data received from the primary molecular process.
If for a moment we think of the colours of birds, of those of a butterfly or of a tropical fish and we compare them to those of the Mammals we will be remain quite deluded. In mammals there are not very pure colours which go from yellowish to reddish, to red-brown, grey and black with a monotony which is only broken by the alternations of tints which occur in spotted, speckled and dappled animals.
Two pigments, melanin and pheomelanin, contribute to this colourationLink 14. If one makes an exception of the haemoglobin of blood, which only in determined occastions rises to the surface with its characteristic colour, we do not know of extractable yellow, red, blue or green pigments which can be classified as individual chemicals: the skin of the monkey Cercopithecus sabaeus only appears green because of a mixture of yellowish and black hair. The blue and green colours of the often changing tonalities of mammals eyes, so wonderfully pleasant to see, are due to an effect of a physical nature or come from the combined actions of a schemochrome and a biochrome.
Melanin and pheomelanin are electro-active materials
The pigment ( BCM ) which colours the skin and hair of mammals is made in a cell called melanocyte (3). The melanocytes originate from cells of the central nervous system during embryo development and their relationship with the nerve cells is clear if one observes the dendritic structure, that is with lengthening similar to filaments. Studies which can be considered definitive have been carried out on their origins. Using mice as experimental animals it was possible to show that only those tissues containing the neural crest, that is the first outline of the nervous system in the embryo, produce cells (melanoblasts) which transform into melanocytes, and, vice versa, that transplanting embryo tissue excluding the nerve cells leads to the normal development of skin and white hair but without pigment production. In the mouse the melanoblasts, which then become melanocytes, abandon the neural crest on the twelfth day of embryo development, while in man the first melanoblasts are observed in the skin of the foetus at about the tenth week of gestation.
Melanocyte is characterised by the presence of numerous organelles or vacuoles at different stages of development. At the start the vacuole (a) is barely covered by a thin layer of semidense uncoloured material which rapidly hardens and increases to take on a definitive form, called premelanosome (b). The premelanosome is, by now, in an organised and specific stage for the production of melanin, in which the enzyme which must start the chemical reaction and the proteic matrix on which the pigment-polymer will grow are found. In the phase (c), called melanosome, an ordered depositing of the melanin starts and proceeds quickly until the appearance of a real black or brown granule (d), in which the main constituent is melanin.
Melanin samples contain all these particles. So eumelanins are artifacts.
In the granule every chemical activity is inactive. It is ready, like a synthetic colour, to be used for the scope for which it was constructed. It passes to the epidermis where there are two types of cells: the keratinocytes and the Langerhans cells. While the function of the latter is not very clear, there is, however, very close activity between the melanocytes and the keratinocytes so that one may, like for pigmented agents, talk of a single system functioning in perfect harmony. As well as receiving the granules of pigment from the melanocytes the keratinocytes also procure them phagocytising portions of dendrites This makes one think that there is a particular biological organisation which integrates the single functions of the two types of cells.
The intensity of the colours of the skin depends mainly on the colour and the form of the granules and on the number and the way in which they are distributed. For example, the difference in colour between Africans and Mongols is due to the fact that the granules in the first are isolated and scattered in the keratinocytes, while in the second group the granules are located in groups in some vesicles of the keratinocytes. Genetic control is probably carried out in a different and complex way. For example, on the matrixes of the melanosome or at a level of a different stage of development of the particles of the melanocyte, or on types of melanins synthesised. Besides specific genes which act on the melanocytes, others may also act with modifications to the tissue which surrounds them.
How tyrosinase acts
The enzyme tyrosinase is found in the melanosomes of the melanocytes and is essential in the synthesis of the melanin. The enzyme, which is also known in the crystallised form, is a protein with a copper base which catalyses the oxidation of tyrosine up to producing a brown or black pigment. If we consider that the tyrosine is a substituted phenol we can imagine, putting phenol in the place of tyrosine for simplicity, that the reaction proceeds along the following course:
Without entering into details on the reaction which is more complex than it appears in the scheme it must be said that the enzyme acts on the monophenol transforming it into diphenol, and successively into quinone. Recently it was found that the oligomers contains one oxygen more than the monomer (23).Link 22
The quinone is the real motor of the polymerisation process, which proceeds until an insoluble granule forms. Only at this stage does the black colour appear. In the case of tyrosine the reactions are more complex compared to the preceding scheme because the alanine chain (-CH2-CH (NH2)-COOH) undergoes several modifications. Tyrosinase is a very versatile enzyme and is capable of catalysing the oxidation of the tyrosine even when this is part of a proteic chain, and probably its action continues through to the intermediate polymers which lead to melanin.
An explanation of why the pigment grows in an ordered way in the melanosome, that is in different and regularly displaced points, can be provided by supposing that the polymers, at a certain stage of their development are anchored to -SH groups in the proteic matrix. A zebra pattern could thus result. In fact, this can be seen by electron microscope.
The absence or the inactivity of the enzyme is the cause of that disease in man known as albinism. This metabolic error, which is congenital, discolours the skin and the hair, makes the eyes sensitive to light and, in general, shortens life. Albinism, that is, the block on chemical reactions which lead to melanin, is also noted in other mammals, but is rather rare in those which live in the wild because they are soon eliminated by natural selection. From a genetic point of view albinism is due to the transformation of an A dominant gene, able to synthesise the tyrosinase, into an a recessive allele which no longer produces the enzyme. Hyperactivity of the enzyme can produce, vice versa, large areas of highly pigmented skin or be associated with those terrible tumours called melanomas which are observed on the skin of a large number of animals, from fish to man.
A difficult formula to determine
In the study of chemistry dogma imposes that the description of any molecule, even for complex molecule, it needs to establish the molecular weight, the nature of the atoms and the bonds which keep them united, and the steric configuration. In many laboratories the aim was to obtain this information even in the case of the melanin.
At first sight the situation does not seem bad. The granule of melanin can be easily isolated, has a well-defined form and varies according to the animal, according to whether it is found in the skin of man, in the skin of bovines, in the feathers of birds or in the ink of cephalopods. Its diameter is such that it is possible to see it with a good microscope.
Later it was observed that the granules are very resistant in oxygen free atmosphere so much so that they have been found in fossils of Cephalopods, fish and frogs from 150 million years ago. If, in the past, a similar life to ours were on the Moon it is highly probable that the melanin would have been conserved more than any other pigment. The insolubility which the pigment shows in every type of solvent is another characteristic which explains how the melanins have even come down to us in fossils. The fact that a solid does not melt makes it very difficult to understand its structure at least in the common sense of organic chemistry, but this is not the only negative aspect which makes it difficult to establish the structure of the melanins. In fact besides being insoluble, they are also amorphous (4). In any case, we know a lot about the chemistry of this pigment, although it is an hard task to write the formula of a single melanin ( granule or particle ). (23)Link 4, Link12
It is formed starting from tyrosine, a very common aminoacid in nature, which transforms into DOPA (Dihydroxyphenylalanine). The Dopa in the presence of tyrosinase or in weakly oxidising environments produces different products among which the 5,6-dioxyindole ( DHI ), a colourless compound which converts very quickly into the corresponding quinone, which easily polymerises following the line of the scheme first shown for the simple quinone.
It has been demonstrated, both directly and indirectly, that in various types of melanin partial structures are present in a relationship which can vary from melanin to melanin and which influence on the physical properties of the melanin. The presence of units, that is of groups different atoms, indicates that the formation of the melanin is a process of oligomers copolymerisation accompanied by oxidative processes. In general, these reactions are no longer controlled by enzymes and the pigment grows in a disordered manner to form the particle.
On the basis of these data it is possible to suggest a formula which qualitatively represents one of the many oligomers of melanin which make up the granule. (New type of oligomers which form the granule of the BCMLink12, Link 19, Link 22)
In a structure of this type the attachment points of the various units a, b, c, d, e, f are arbitrary even when taking into account the information gained by their chemical demolition. A polyene structure of the type described by Little is always observed (20). Probably the unit c represents the most conspicuous part of the molecule (5), while the other units are only a minor part. The relationships among the various units can, however, vary according to the biological source from which the melanin comes, like for example hair or fur, skin or melanocytic tumours New structures suggest melanin as acetylene-black derivatives.. In the latter unit e is very numerous, which should mean that the biogenesis of tumour melanin may follow a different course to physiological melanins and is a fact worthy of being examined in depth. Finally it is to be recalled that a melanin is not sufficiently described if the full elemental analysis is not considered.
It is no longer possible to attribute these molecules with the classical meaning which the term chromophore has for the common coloured molecules. While for the latter we say that they are red, yellow or viola, because a determined chemical grouping is present, for the melanins we attribute colourations of brown, red-brown and black to the forms of the granules, to their size and to the number of the granules.
In the mantle of some red-brown sheep the granules have different dimensions from that of black sheep, in grey cats the granules are distributed in a particular manner. In chestnut hair, the granules of melanin are transferred from the melanocyte to the hair in groups, under genetic control. In man and in the horse a grey colour is, instead, due to the mixture of black hair with white hair.
The melanosomes of the melanocyte of races with blond hair are not completely full of melanin as occurs for the granules of races with black hair, they have, rather, a laminated structure similar to that of the premelanosomes, and are less numerous.
There are not chemical and physical methods which lend themselves to the rapid identification of the melanin, apart from the black colour. One needs must recur to the laborious method of degradation and to the recognition of 2,3,5-pyrroletricarboxylic acid and of 5,6-dihydroxyindole (DHI) which are characteristic demolition products.Useful parameters to be determined are EPR, NMR, MALDI spectra.
Changes of colour
For man a change of colour is almost always a dramatic fact. Modifications in the colour of the skin often indicate serious illnesses. The sudden darkening of a mole can be the sign of the invasion of cancer. Hair turning white, phenomenon in which the activity of tyrosinase slowly decreases until it stops completely, is a sign of decline. In the picture of alkaptonuria, a metabolic illness of a genetic nature, sweat, the nails and the skin can appear coloured. Some parts of the skin take on a dark blue colouration and the sweat can be red because of deposits of excretions, respectively, of polymerised homogentisinic acids (degradation products of tyrosine and phenylalanine). Less worrying and rather rare is the phenomenon which can make colour the sweat red, yellow, green and even black because of a probable dysfunction of the membrane together with an excessive ingestion of food or coloured products. As an aside, and for curiosity, we may note that the hippopotamus normally sweats red, because of a pigment, as yet unstudied, but which is probably of a polymeric nature, given that it is not dialyzable and, with alcohol, precipitates from an aqueous solution.
The only change in colour which can be considered a frequent and normal phenomenon is that which goes under the term suntan and is very visible on the skin of the white races. When radiation hits the skin a part of it is reflected, a part adsorbed and dispersed, and a part penetrates beyond the horny layer.
The horny layer, composed of cells of a thickness of 10-20mm, has the capacity of reflecting light and also of partly absorbing ultraviolet radiation which has wavelengths between 260 and 290 nm, because of the presence of free components (histidine, peptides, cholesterol, phospholipids). The thin underlying layer formed by Malpighi cells is composed of proteins, fats, nuclear membranes and more or less pigmented granules (melanosomes). This layer serves to disperse the low wavelength radiations which have managed to pass through the horny layer. In particular the granules of melanin absorb both ultraviolet and infrared radiation and visible radiation. Without the protection of the pigment, which in dark skin forms more numerous granules which are also closer together and almost forms a barrier, a considerable fraction of the radiation between 240 and 300 nm would reach the papillae of the skin. In less pigmented skin, therefore, the light and in particular the ultraviolet rays can reach the derma, site of important biological reactions. The radiation transforms many molecules, and in a special way those which possess -OH groups (hydroxyil), into free radicals, which, finding themselves in an anomalous state of valence, are extraordinarily reactive and combine with every other type of molecule without any longer obeying the cellular laws.
While men and women overcome by a sudden melanic raptus lie softly extended on the roasting sands, the ultraviolet rays penetrate into the most vital parts upsetting the ordered procedure of the metabolic production line. The signs of alarm in the organism are clear: painful red skin, boils, shivering, fever, nausea, sense of prostration and peeling. Fortunately, the solar action sets off an antiradical operation at the same time (6). The tyrosinase enzyme which is found in a sort of lethargy in the melanosomes suddenly becomes active. The skin pigments and the men and women gets tanned. A quite well-credited hypothesis to explain the phenomenon in molecular terms is that in white skin there are substances containing -SH groups (sulphydrilics) which link to the copper of the tyrosinases and make them inactive. The ultraviolet light manages to unblock the inhibited form, oxidising the -SH groups into SO3H (sulphonics) . The result is that a higher number of granules are synthetised are transmitted to the superior layers and in the end they form an efficient shield against almost 95% of the radiation. However, melanin is not the only defence of the organism against radiation. Further protection is, in fact, obtained both by the thickening of the horny layer and because of the favourable conformational action of urocanic acid. This acid, which is found in the trans form in the epidermis, absorbs ultraviolet rays and transforms into the cis form and can then give back the absorbed energy, which is no longer dangerous, in the inverse cis / trans passage.
It is also possible defend oneself against the dangers of solar light by the use of artificial products like p-aminobenzoic acid and benzophenone which absorb ultraviolet radiation, or zinc oxide and titanium oxide which reflect the light completely. All these products, under a phantasmagoria of names, are part of sunburning cosmetics. One more refined and physiological way of increasing the pigmentation would be the use of injections of the hormones which are usually indicated by the sign MSH (Melanocyte Stimulating Hormone).
The changes in colour in the other mammals are conspicuous and of a different meaning. The ermine Mustela erminea has a dark fur in summer and white fur in winter. This is due to temperature. In fact in hot environments the ermine grows and proliferates producing dark fur also in the winter period. In the weasels Mustela cicognanii and Mustela frenata the colour of the fur depends on light, that is, on the different lengths of the summerís and winterís days. It is probable that both temperature and light are factors which act together on hair colour in other animals. The domestic rabbit of the Himalayas is born with white fur, but then the points of the nose, of the ears, of the tail and or the paws become black. It is curious to observe that the extremities which are exposed to a lower temperature than the other parts of the body. Also the Siamese cat is rich in melanin in the colder zones of the body. The Alpine hare Lepus timidus has several mutations in relation to temperature, light and hormonal influences. The white of December to April is progressively substituted by grey and brown hair. These changes of colour allow the animal to adapt to the colour of the environment and constitute defensive system against enemies.
Red feathers pheochromes, red crest hemoglobin,
black feathers melanin, brown pheomelanin
Most of the reddish and red-brown colours of mammal hair are due to pheomelanins and pheochromes (7) (21)Link 14. Freckles on human skin are also coloured by these pigments. It is probable that one also sees tonalities of colour which go from yellow towards pink according to the concentration and the forms of the granules of pigment. The colours are never pure and lively like those imparted to different animals from other biochromes like, for example, the carotenoids.
In many mammals, but not man, the hair can be coloured either by melanin or by pheomelanin. The two pigments can also be present in the same hair.
The pigmentation of a a black or red hair is made over several phases. The melanocyte or pheomelanocyte produces the granule of pigment (of variable size and shape) which is transferred into the cells which form the hair. The cells which have received the pigment are then elaborated by the papillae of the hair which produces all the structural elements of the hair and the hair itself.
Pheomelanin is also formed starting from tyrosine. When this arrives at the dopaquinone, however, this reacts with cystein forming the main product of 5-S-cysteinildopa, a recently discovered aminoacid, which is the real precursor of pheomelanin (8) (Link14).
In 2001 it was discovered that melanins arise from cyclodopa whereas pheomelanins are derived from benzothiazinone (21),(23).
This genetically controlled reaction decides if a man will have red or black hair, if a dog or a cat, or another animal will have a fawn or black coat.
The pheomelanin is more or less easily freed of keratinous material and isolated from materials of various origins (hair, fur, feathers) by extraction with alkalis. It is a complex mixture of pigments linked to proteic material, or not, having a variable molecular weight. One of these pigments, of a red-orange colour in the crystalline state, and which because of its physical properties is more easily isolated than the others, has a structure which has never been found previously in nature. In an alkaline environment the pigment shows a maximum absorption at 452, 327 and 240 nm in its spectrum and possesses the interesting characteristic of converting, by heating with acids, into a pigment of an intense red-viola colour.(8).
From formulae of structure one sees that this pigment derives from cystein and from dopa according to a process which consists in the closure of the cysteinic chain on an oxyhydril of the dopa and on the benzenic ring with the formation of a unit of a benzothiazine type and successive bonding of two to these benzothiazine units.
The other pigments, of red-brown colour, which accompany the yellow-orange compound are seen to have more complicated structures. A part of the molecule is formed by units characterised by the presence of thiazole rings, presumably formed by restricting the thiazine rings and the pyridine type rings by closure of cycles of the alaninic chain (-CH2-CH(NH2 )-COOH)
From a chemical point of view, the structure of the melanins and the pheomelanins differ profoundly, while it is possible that the two classes of pigments are biologically correlated: for example one can think of a single enzymatic system which can operate alternately on the dopa or on the mixture dopa + cystein, while the control on the formation of melanin and pheomelanin can be carried out by the melanocyte or by the premelanosome at the level of the membrane.Melanin precursor is cyclodopa whereas pheomelanin has a dibenzothiazine (derived from cysteinyldopa ) precursor.
The granules of the two types of biochrome are different. In the hair of the guinea pig, the granules of melanin have the aspect of rods quite similar to one another while those of the red and yellow pheomelanins are of a spherical or granular form. In the first case the pigment is orientated on a proteic matrix, while in the second case no particular disposition has been recognised (9).
The colourations of human hair are varied: carrot red, orange, Titian red, red-brown. This variety of tints may be explained by the quantity and the type of pheomelanin present in the hair. Less probable is that these colourations can appear modified by the melanins, as happens in other animals, even though in the individual the browning of red hair with age is a frequently observed fact.
Individuals with red hair can find themselves in a biological disadvantage compared to those with black hair because the red pigment does not offer adequate protection from solar radiation. The irritable character which is often commonly attributed to those with red hair is, perhaps, linked to a particular photosensibility of the pheomelanins and of their metabolites. What are the environmental and biological conditions which have determined, among our ancestors, the synthesis of a red pigment? And, what functional role did this pigment play in the past? (22) (23)
Haemoglobin as a pigment
As well as having the vital function of carrying oxygen from the lungs, through the arteries to tissues the haemoglobin which colours the blood of animals red plays a more modest role as a pigment of exhibition in mammals.
In man the red colour of the cheeks is due to the very thin skin which allows the haemoglobin to be seen. In other animals haemoglobin contributes mainly to the colour of the skin but is masked by the presence of melanin, by the layer of keratin and especially by hair which, for example, in bears constitutes an impenetrable coat. Its rosy or red colour can however be observed on the tongue at the tip of the nose, inside the ears and on the buttocks of many mammals, in all those zones, that is, where the hair or the mucous is very thin. The African mandril and other apes have red areas of the body because of a high vascularisation of the skin and other red-bluish parts because of a combination of the red of haemoglobin and the black of skin melanin; other zones, like those of the buttocks, are clearly blue thanks to the Tyndall effect of a schemochrome which has a structure which has not been studied in depth.
One class of pigments which are affine to the chromophore system of the haemoglobin from the structuristic and biogenetic points of view are the porphyrins (see Birds). These pigments contribute rather little to the colour of mammals but one interesting case is known from the teeth of the Coypu and from the bones of the American squirrel Sciurus niger which are a brown-reddish from a porphyrin (uroporphyrin). The pigment can be shown by irradiating the bone tissue with ultraviolet light since the porphyrins become fluorescent. A singular location of the porphyrin, visible with ultraviolet light, is that of the protoporphyrin IX, degradation product of haemoglobin, which is found accumulated in Harder's gland (a gland associated with the lacrymal apparatus of the rat).
Because of a metabolic disturbance, in general hereditary, also the teeth and the bones of man can have porphyrin colour. However, this is a serious illness which, besides presenting different symptoms and producing serious suffering, makes the patient strongly photosensible because of the porphyrin.(22).
Animal coat patterns
Mammals exhibit a great vatiety of coat patterns (leopard, cheetah, jaguar, giraffe, zebra, etc.) Mathematical models are consistent with the distribution of the spots, predicts that the patterns can take only certain forms, implies the existence of developmental constraints (124).Melanin and pheomelanin contribute to the animal coat patterns.
The eye of the galago
Lemurs have grey, brown or rust coloured fur because of the presence of melanin or pheomelanin. These animals strike us because of their large yellow or reddish eyes and because of their eyesight which is also very accurate at night. If struck by a shaft of light their eyes shine like two lights in the dark. The yellow pigment of the Galago crassicaudatus, constituting the tapetum lucidum behind the retina, is crystallised riboflavin. Riboflavin is known as vitamin B2, and it is a real surprise to find it accumulated in the eyes of the galago.
The scientific drawning
Reptiles and amphibians . P.H.Gosse watercolour ( Endeavour 8, 70-79, 1949).
From the Historical Archives of Zoological Station of Naples.Famous draughtmen or aquarell- painters,were Leonardo da Vinci, Salviani, Ruini, Bewick, Giltsch, Gosse, Leidy, Megnin, Fowler, Lankaster, Goodrich, Thompson, Curtis, and Manzoni, Merculiano, Salfi, Serino of the Zoological Station of Naples (1845-1970).
The African bat Lavia frons spreads a yellow dust produced by glands which are found on the lower part of the body on its hair, as if it were a cosmetic. It is difficult to say though if such behaviour is intentional as it is in man.
The history of colour as ornamentation has ancient origins and is full of meaning. Colour and coloured patterns had great importance among primitive races, and the ancient Romans, especially in times of war. Julius Caesar was impressed when he met the first Britons with blue and viola skin (10) and thought that they painted themselves to scare off enemies.
The art of colouring oneself, very common in the past, still survives today among the Maoris, the Papuans, the Japanese and in some African tribes, even if the primitive meanings are being lost.
Australian aborigines paint their faces with stripes of yellow or red ochre, charcoal, soot and chalk for the ritual which signs the end of puberty. Still today the Brazilian indians paint their bodies viola and brown, using vegetable extracts, and in particular make black marks under the eyes to express sadness and red to express happiness. A refined polychromic cosmetic with a message about the feelings is a notable advantage in social relations, but we think that man in his hypocrisy is reluctant to uncover his own sentiments.
In the western world modern men, except in a few cases, do not paint themselves while for women colours, unlike in the past, have the sole scope of esthetic pleasure and sexual attraction.
The most used colours are without doubt red and black. Lipsticks are made with potassium eosinate, white wax and almond oil or very fine powder of silk coloured by eosine and incorporated in wax. Other pigments which are used are alizarin lacquers, cadmium yellow and rhodamine myristate, while the pearly aspect comes from extracts of fish scales. Naturally there are differences from one lipstick to another, some of which even change colour according to the pH of the lips.
Other coloured cosmetics are hair dyes, face powder, cosmetics for the eyes and nail varnish. Among the colourants of hair we have henna, a vegetable extract of the Lawsonia alba containing naphthoquinone lawsone, next to products of synthesis derived from p-phenylenediamine. While these colourants penetrate the hair others on bases of silver or copper form a thin layer on the hair and also give the colour a metallic shininess. Face powder is a mixture of talc, chalk, kaolin, zinc oxide and magnesium stearate, all coloured and perfumed according to need. Cosmetics for the eye-lashes are generally carbon of bones with an oily base while eye shadow has a composition substantially similar to lipstick with the frequent addition of metallic dusts of copper or of aluminium to increase the brightness. Nail polish is basically a colloid of butylic alchol and ethyl acetate, with the addition of pigments chosen from the vast array of tones offered by modern industry: a little ammoniac extract of fish scales gives it the mother-of-pearl appearance of the nails.
A cosmetic to be taken internally has not yet come into use even though it is possible to colour the hair of albino mice orange by administering a chemical substance like 9-phenyl-benzoisoalloxyzine, and of transforming, in part, the very black ink which is found in the sack of the squid into a red-brown coloured pigment by introducing cystein into the blood circulation of the animal (11). These results, which may be enriched with new experiments, are in agreement with the well-known capacity which the precursors of melanin have for copolymerizing with other organic molecules.
The art of tattooing (from the Polynesian tatu = wound) consists of the perforation of the skin and the successive introduction of coloured substances. Much used by Polynesians, Maoris, Burmese, Chinesea and Japanese it was brought the Europe by sailors. Among Polynesians tattoos are made starting from the age of 12 and are a sign of puberty. The most extended tattooing is carried out in the Marshall Islands where all the body is covered with black and red colouration. The skin is perforated with needles or with special sharpened apparatus which are applied and hammered while they are hot, in a deafening noise of drumming and singing which cover the cries of the unfortunate. The Eskimos operate in a different way passing a thread covered with soot under the skin. After being taken out this leaves black lines. The Australians practice scarificazione: cutting the skin and filling the wound with coloured clay and adding ashes to aid scar forming. The meaning of tattooing is quite different according to the place and the time in which it has been practised: esthetic, erotic, sign of power, sign of vendetta, or memory of an oath or as recognition. More rationally, it was practised in the Second World War in the American army to indicate the blood group of soldiers.
The message of colours
Colour provokes many thoughts. Many of these must be linked to a memory which has its prehistoric roots, where colour played an important role in the life of man. Colour still serves us today in the choice of food and the environment in which to live. Naturally, the "coloured" message is elaborated in a different way according to the specialisation of the person. The expert values its fertility from the colour of the countryside and what to cultivate from the colour of the soil. Some plant diseases are identified by the colour. The colour of the patient helps the doctor in his diagnosis. The chemist takes information on the nature of the substances, from the colour of his test tubes, classifies them and establishes if a reaction has happened or is going well.
There is a vast literature on the reactions of man to colour. The entire organism appears to be influenced by colour. Different types of emotion and levels of activity may be linked to the intensity and the wavelength of light. The colour purple is majestic and therefore ends up by becoming unbearable, yellow is lively, green relaxing, blue partially diminishes activity. In green the artist feels fecundity and hope; in blue faith, immortality, transcendence, in red passion, power, sensuality, in yellow intelligence, knowledge and wisdom and depending on the tone falsity or serenity. These are primitive messages. Green; nature and spring. Red; blood. Yellow; gold.
The pigment of the skin, like all the black bodies, reflects only a small part of incident light, which is therefore mainly transformed into heat. In a significant experiment one dyes a white melon seed black and plants it next to a white seed. The coloured seed germinates first.
The strongly pigmented skins "are hotter', maintaining the absorbed heat longer and have a more difficult hydric exchange than white skins. The quantity of melanin can also influence the production of vitamin D.
These qualities of melanin are the basis of the hypothesis put forward, also if not completely shared, that the whites may descend from blacks. In prehistoric times large masses of negroes coming from Africa passed the 40th parallel and settled in Europe. Here they found very different conditions of life for light, humidity and temperature. On the one hand the European sun, poor in ultraviolet rays, and on the other the reduced possibility of these to penetrate to some less pigmented parts of the body, like the insides of the palm of the hand and the sole of the feet.
The generations born in Europe soon found themselves at a disadvantages, while cases of rickets became ever more frequent because of the relationship light/melanin. Since the only hope of survival was to process the excess melanin, a process started at a genetic level whereby the synthesis of the granules of melanin was blocked or reduced. This led to a gradual lightening of the skin until the almost total disappearance of the colour black. The situation in which the blacks of America, coming from Africa only recently, find themselves is different and there are different factors which have brought their problem to the surface. Even though it is true that the violent and disorganised character and sudden of the revolts of American blacks against the whites may be due to the electrical and sound conductivity of the pigment cell.
Fascinating and delicates colours of hummingbirds
(life-size) from south America
Melanin, Carotenoid, hemeglobin of the crane
Balearica pavonina from West Africa
The colour of Birds is mainly due to biochromes and to schemochromes of the feathers which cover the integument (skin) where the colour is only rarely visible. No animal shows such beautiful and full colours, such delicately shades, with brightness and iridescent, as the Birds. The fall of the feathers and their periodic renewal (moulting) can substitute the livery of the birds with a colour which is better adapted to the environment in which the animal lives for a certain period. In Birds colour is important for the recognition of the species, of sex, age and the way of life.
The parrot Ecletrus roratus: Different sex different colours
The livery of the male bowerbird (Ptilonorhyncus Violaceus) is deep, irideseent sating blue coloured; females are dark green on the back and spotted yellow-white on the underside.
The control of colour in Birds is carried out in differing ways. In the Livorno hen a brown colour is seen because of the action of ovarian hormones, as demonstrated by the fact that if the ovaries are eliminated it takes on the brilliant colours of the male. In the pheasant the colour is influenced by ovarian hormones, while the pattern of the plumage does not depend on hormones but on genetic factors. In the sparrow only genetic factors control the colour and the type of plumage.
Except in some rare cases only three types of biochromes colour the plumage of birds: melanin, pheomelanin, carotenoids.
Melanin and pheomelanin.
Black, brown, red-brown and reddish colourations of the feathers and integument, and the beak of Birds are due to melanins and pheomelanins (21) (Link 14).
The pigmentation of the feathers comes in a similar way to that of the skin or the hair of the mammals: the melanocytes produce the granules of pigment and these are then transferred to the cells which form the keratinised part of the feather. While the quill ( calamus) is not pigmented, the barbs (vexillia) and the rachis are coloured as occurs for example in the feathers of the turkey.
Melanin also colours the skin, as in the hen of the race Silky where the phenomenon can be observed in a clear way because of the contrast between the black skin and the white feathers, while the red-viola lappet appears so because of a physical effect of the black skin and of blood. In many birds the brown and black colours of the beak is due to melanin: the granules of the pigment form thin alternating layers in the corneal plates which make up the sheath of the beak. The small Australian parrot has a blue or brown coloured beak according to whether the animal is male of female. It is interesting to note that if the beaks of some males are dyed brown one sees the extraordinary spectacle of males courting other males, and more precisely courting those which have dyed beaks. In these birds the beak is coloured brown by the melanin while the blue colour is the work of a schemochrome.
The red-brown colour (12) of the New Hampshire hen is due to the presence of gallopheomelanin. A mixture of 4 macromolecular compounds which are similar to each other is found on these feathers.
Gallopheomelanin-1, the most abundant pigment can be separated quite easily from the proteic material which accompanies it. Its average weight is of about 2000, gallopheomelanins-2, -3 and -4, are chromoproteins containing about 60% of a protein which differs from the keratin of the feathers because of the absence of the cystein as the sixth aminoacid. If we consider the general structure of gallopheomelanin-1 more closely (structure determined mainly from oxidative demolition products) we note that carboxylic, primary aminic and phenolic functions are present in it.
From the degradation products (fusion with alkalis and oxidation with H2O2) one notes the absence of pyrrolic and indolic derivatives, products characteristic of the degradation of eumelanin. This proves that the pheomelanins are not structural variants of eumelanins but are charaterized by a dibenzothyazine system .
Gallopheomelanins-2, -3 and -4 give the same degradation products obtained from gallopheomelanin-1 which suggests that they have the same general structure and probably differ only in their molecular weight and the attachment to the protein.
Pheomelanin is also responsible for the yellowish, pink and pink-brown colourations which are seen in other Birds. Although there is no chemical proof, it is generally believed that that the delicate and pink-brown shade of the breast of the chaffinch Fringilla coelebs is to be attributed the granules of pheomelanin deposited in interspersed groups with regular spacing which reflect white light. Tonality and different colourations, both of melanin and of pheomelanin, are certainly explained by the different size of the granules, their number and their dispersal rather than by the difference in the chemical structure of the pigments. The colours of the band model were taken into consideration recently (21).
Many of the yellow and red colourations of feathers are due to carotenoids. The pigments enter the animals through the food chain. They are found in the cells, at the start of feather growth, in fatty drops and when the hornification starts they leave the pigmentary cell and spread to the keratin. The carotenoids link to the proteins making a carotenoid-protein complex which possesses a different colour to that of the free pigment. For example, while the free carotenoid is yellow or red, in combination with the protein it can be blue. Naturally the combination also modifies the solubility of the pigment, in the sense that this when it is free it is soluble in solvents of the fats and insoluble in water, while when it is combined the solubilities tend to invert.
The carotenoids, which are generally formed by 40 atoms of carbon, have a characteristic chromophore system from double bonds alternating with simple bonds distributed on a branched chain. At the extremities of the chain they carry, almost always, two cyclohexenic trimethyl-substituted rings which are often oxygenated.
The carotenoids can give the feathers yellow, orange, red and viola colourations and in combinations with proteins or schemochromes violet, blue and green. They are soluble in the common aprotic solvents (that is ether, benzine, carbon tetrachloride, etc.), while the are insoluble in water, also in the presence of acids and alkalis. They are resistant to alkalis and more or less stable to atmospheric oxygen and which may sometimes decolour them. They give blue colourations with H2SO4 and with antimony tricloride, but the reaction is not to be considered decisive for recognising a carotenoid. The hydrocarbonic carotenoids like b-carotene are soluble in ether and ligroin, while those with oxygenated functions dissolve better in methyl and ethyl alcohol.
Purification of the carotenoids extracted from tissues is made using columns of glass filled with calcium carbonate, magnesium oxide, calcium hydroxide and aluminium oxide in the order chosen from one time to the next according to the absorbtion force required.
The animals are not able to synthesise the long chain of carbon atoms of the carotenoids but are able to transform them, in general, introducing oxygenated functions (-OH, CO etc.) into the cyclohexenic rings. For example, in feathers one findsb-carotene, which as the word says is the pigment of the carrot, next to zeaxanthine, cantaxanthine and rodoxanthine, all containing oxygen. In general in the animals one finds other pigments which do not contribute to the colour, given the small quantities, and which are only intermediate products, next to the carotenoids, or next to the carotenoids introduced by food. There are factors of uncertainty regarding the mechanism by which the oxygen is introduced into the molecule: that is, whether it comes from atmospheric oxygen or from water, whether the mechanism is under enzymatic control or is a catalysed reaction, provoked that is by light. It is also possible that we are dealing with a complex mechanism in which various factors act together. If one bears in mind that the laboratory synthesis is very often realised in nature, it is worth recalling that if one treats the b-carotene with N-bromo-succinimide (NBrS) and acetic acid one can obtain cantaxanthine, as show the reactions illustrated in the following scheme:
The red colour of the feathers of Lanarius atrococcineus, Phoenicirens nigricollis, Ajaia ajaia, Rupicola rupicola, Guara rubra and Pyrrhula pyrrhula are due to the accumulation of rodoxanthine, cantaxanthine and astaxanthine (see Invertebrates). The yellow, orange and red colours of the woodpeckers Colaptes cofer and Colaptes auratus, of Melanerpes erytrocephalus, of the weavers Euplectes franciscanus, Euplectes orix, Euplectes nigroventis, Euplectes afran, Euplectes taha, Ploceus cucullatus, Oriolus xanthornis, of Pyroderus scutatus, of the fulmar Fulmarus glacialis, and the brilliant colour of the beak and the feathers of the toucan are also due to the carotinoids. The blue, viola and red colours seen in the barbs and feathers of the western pigeon Ptilinopus are due to the differential distribution of the pigment and to the thickness of the keratin. It is interesting to note that when one varies the substratum of the elution medium in chromatographic experiments on columns the rodoxanthine presents different colourations among which red, violet, blue. The Xipholena lamellipennis has feathers of a dark red, almost black, colour due both to the concentration and the crystalline form of the carotenoids. In fact by simple grinding of the feather, pulverising crystals, as happens often in the laboratory, it is possible to modify the tonality which appears red.
Unlike the wattle of the Silky hen the red skin under the eyes of Lyrurus tetrix and Tetrao urogallus are due to carotenoids.
In flamingos, like Phoenicopterus ruber, the main pigment is cantaxanthine which is synthesised starting from alimentary carotenoids. The colour of the feathers is in strict relation with the diet: the birds appear red when they eat small crustaceans rich in carotenoids, while they can become completely white if this food is missing from their diet. The phenomenon is always reversible.
Canaries have a various tones of yellow and orange, due to lutein and canarixanthine, which has a structure not very different to other carotenoids but which not has yet been clarified in detail. Often the feathers of these birds lighten because of a diet where carotenoids are excluded, while the habit of adding small quantities of pure carotenoids, which can easily be found in the shops, to the food gives surprising results.
The paridae tits have an olive-green plumage because there is a melanin (acetylene-black?) at the top of the barbs, while at the base one finds a yellow carotenoid. For the same reason in the great tit Parus major the dorsal feathers appear of a blue-grey-greenish tone, and those of the greenfinch Chloris chloris appear greenish. The green of the tropical bird Zoosterops comes from the fact that the barbs are yellow because of a carotenoid, while the barbules are black because of melanin. In the tropical America Tanagra lutea the olive-green effect is obtained by the superposition of the yellow feathers of the wing on the black feathers of the back, while the olive-green thighs of the Tringa nebularia have this colouration because a yellow carotenoid covers the melanin stratum of the skin. The typical green due to a blue schemochrome and a yellow filter made of a carotenoid is represented in many birds.
The green plumage of the south east Asian crow Cissa chimensis becomes blue if exposed to the light because of the loss of the carotenoid which acts as a filter. The birds which live in the depth of the forests are green, while those which prefer light without shadows are blue.
In the lorikeet Trichoglossus flavicans of the Pacific islands the feathers can be intense green, olive-green or yellowish, and the phenomenon is interpreted as being due to the variation in the thickness of the yellow filter. It should be remembered that in general the olive or darkish green is not produced by the Tyndall effect added to a yellow filter which produces, rather, a pure green, but from the simple superpositioning of yellow and black feathers and hairs.
The beautiful red mark, common to other birds, which flecks the yellow beak of seagulls is the product of carotenoids. This mark plays an important role in bringing up the young, in that the babies hit it to ask for food
The uropygiale gland of the great Indian horhbill secretes a rich oil of carotenoids with which the bird colours itself. Using the beak with exquisite art it paints the edges of its wings and the feathers at the end of the tail, as if using a lipstick, the beak often repeats the operation so as to maintain the lively colour.
A more unique than rare pigment
The twelve or fourteen feathers of the wings which stand out for their magnificent purple viola colour lose their beauty as soon as they are wet, rather they discolour if they are touched and stroked by a finger"
"A couple of these birds coloured the contents of an average sized recipient in such a notable way during a bath so that the water seemed a weakly pink coloured ink. While the feathers were wet their red-purple colour took on a strong blue tone, dried again they shone newly in their original purple tint. In the zoological garden of Amsterdam a turaco was struck by convulsions and, as is usually done in these cases, was sprayed with cold water. The bird remained lying in the position in which it had fallen, survived for another few hours and then died. It happened that one side dried again while the flank resting on the ground remained wet. Therefore, it was noticed that while the red colour of the wet left wing had become blue the right wing maintained its beauty. Washing with water did not have the least influence on the feathered layers, but as soon as a bird is immersed in diluted ammonia or in soapy water one can note how the wings discolour (A. Brehm-Tierleben, 1829-1884)"
The turaco of the Musophagea family (from the Latin "which eat bananas") lives in the forests of central and western Africa.
It has green, blue and rust coloured feathers. The secondary feathers can also be a bright red colour with a dark border. The crest on its head is green or black as in the giant turaco Coritheola cristata. The blue colour is due to a schemochrome, the green to a schemochrome modified by a yellow pigment and the black to a melanin. The red pigment is, instead, from a biochemical point of view, a real surprise. One is dealing with a cupric complex of uroporphyrin-III which is easily extractable, like other porphyrins, with diluted ammoniac and is characterised by a spectrum with absorption maxima at 526 and 563 nm. This electro-active pigment called turacine is not found in other birds.
It has been said that one can extract a pigment from the green feathers of the turaco, which would be the first extractable green pigment from the feather of a bird. The pigment has also been given the name, turaco-verdine, but the traces of its chemical structure are mysteriously lost when one consults more recent literature.
This is therefore a more unique than rare example of a visible pigment of a porphyrinic nature. Haemoglobin, instead, contributes to the colour of birds, as in mammals, and in some cases it does so in a marked way. A lively red colour stands out in fact in some parts of the body of birds as for example in the lappet of the turkey.
From the porphyrins to bile pigments.
The porphyrins all derive from the macrocyclic system called porphyne. The various porphyrins which are obtained substituting different atomic groups in the numbered positions indicated in brackets next to the number which indicates the position that such groupings occupy.
The four typical spectra of porphyrins
They have a characteristic spectrum in the visible zone in which an intense violet band, called the Soret band, stands out. The intense fluorescence, which disappears when they are combined with proteins of metals, as in the case of haemoglobin, allows the recognition of small quantities (in the order of gamma) of porphyrins in biological sources.
Among the porphyrins found in the shells of eggs there is the protoporphyrin-IX (the same as can be obtained from the haemoglobin of blood). Bile pigments can be derived from this porphyrin. If the cycle opens starting from the carbon atoma, one obtains a new system in which the rings are found in linear chains.
The nomenclature to distinguish the various pigments derives either from the bilenone system or from the bilene system. Naturally the various substitutions which are found on the porphyrin are also met frequently in the biliary pigments. For example, if we observe the formula of biliverdin it is easy to recognise that all the substitutions of porphyrin-IX are conserved in the biliary pigment.
If the first porphyrin was synthesised in the pre-biological era, as some claim, the bile pigments formed before the Earth's atmosphere became oxidising. Effectively, starting from the porphyrins it is possible to pass to pigments very similar to natural pigments, by bland oxidation.
The name of the bile pigments derives from the fact that some of these pigments, like biliverdin (green) and bilirubin (red) were isolated for the first time from bile. The bile pigments treated with fuming nitric acid give a series of blue, purple, red and yellow colourations, which allow their recognition and allow distinguishing among them. The Gmelin reaction is due to an oxidation reaction and rearrangement.
The bile pigments can produce a vast range of coloured tones according to the level of dilution or, as happens also with the carotenoids, change colour according to whether they are free or combined with proteins. Biliverdin has been isolated in the blue eggs of some seagulls, while in the green egg of the emu, both biliverdin and bilirubin have been found. It is not known if these pigments or the porphyrins have played a role as part of the calcification and if they have a role in the formed shell.
In the birds numerous colours can be present at the same time. In the Bengala pitta the colour of the black feathers is due to melanin, the red and yellow of feathers and the beak to carotenoids, the red-brown to pheomelanins, while the white, green and blue feathers appear because of the effect of schemochromes.
The plumage of the humming bird cannot but provoke an intense emotion.
The ruby red colour, sometimes united with violet flecks, and the aquamarine blue are indescribable colours which are not observed in other birds and neither do the most perfect colour photographs manage to faithfully reproduce them. The green with bronze flecks and the dark emerald green, like a Brazilian stone, are rarely visible in other Birds. In the Panterpe insignis all the colours of the rainbow are represented. The very fast flight, the sudden changes in direction remind us of those of the insects and contribute to making their colours changeable, varied and extraordinary. The shades of colour are the fruit of a knowing dose of carotenoids and melanins on the microscopic lamellar structure of the plumage, which disperses light. The green barbs are jewels of architecture furnished with small quantities of black pigment on the inside and with a yellow on the outside. Using a solvent like carbon disulphide and acetic acid, the yellow pigment can be removed and the feather appears blue, since the honey-comb cells are a fine sponge-like material they produce the Tyndall effect. Vice versa, if one deposits a yellow pigment in a thin film on a blue feather, (for example allowing an ether solution ofb-carotene to evaporate), the green colour reappears.
Parrots present strong yellow, blue, red and green due both to a schemochrome and to a carotenoid, but some yellow or red colourations do not seem attributable to one of the classes of biochromes noted among birds, although the problem of the structure of the pigments has not yet been studied in great depth.
Melanin and pheomelanin are the biochromes of the birds. Schemochromes, which are rare in mammals, are frequent in birds and the beautiful green and blue colours of their plumage are a convincing testimony.
Although the reptiles often present quite vivacious colours there is no extended study on the chemical nature of the pigments. It is presumable from some data in our possession that the brown and black colours are due to melanin but information about the presence of pheomelanins is missing.
The sea-water snake Laticauda colubrina
The yellow and red colours are due to a carotenoid and a pterine and the white to a deposit of guanine or leucopterine. The blue colour is of a schemochrome and the green comes as an effect of a yellow pigment with a blue schemochrome. In the Cheloniae (Tortoises) and the Loricates the colour is different mainly because of granules of pigment localised in the horny cells of the scales while in other reptiles the pigment is found in the chromatophores of the skin.
Some reptiles, among which the chameleon, are able to change their colour rapidly. This extraordinary ability occurs through a new type of pigmented cell called a chromatophore. According to the colour of the pigment produced the cell is called a melanophore (black) xanthophore (yellow), erythrophore (red) or leucophore (white). In these cells the granules of the electro-active pigment can move, for example from the edge to the centre and vice versa, producing variations in the colour of the skin and in the coloured images so that, in extreme cases all the aspects of the animal are modified.
The movement of the granules is controlled by the central nervous system or by the hormonal system or by both systems. The substances with hormonal action are of a proteic nature, like MSH in the pituitary gland, but can even have a simple chemical structure like the catecholamine. Adrenalin, for example, is able to cause the movement of the grains. In the reptiles in conditions of repose the pigment is more or less evenly spread and in these conditions the skin is darker, while under nervous stimuli provoked by different physical factors like light and temperature, they concentrate and make the skin appear lighter. Later, if necessary, an appropriate dedicated mechanism controlled by the nervous system allows the pigmentation return to the starting position rapidly, while in less extreme cases the pigment moves slowly inside the chromatophore. Sometimes it is necessary for the animals to maintain the response to nervous stimulus, that is, a certain colouration or coloured form, for a longer time, and in such cases hormones of a proteic nature produced by the pituitary gland intervene. Through these mechanisms the chameleon, under the action of light and temperature, changes its colour and its appearance in the extraordinary way which has made it famous.
The carotenoids have been isolated from the serpents Tropidonotus natrix, Elaphis quadrilineatus, Callopeltis quadrilineatus, and Rhinechis scalaris, from various species of chameleon, from the small Japanese tortoise Chrysalis scripta elegans, from the waxy yellow-brown nuclei of the skin of the iguana Ctenosaura acanthura. The coral serpent, with its lethal bite, feared by birds as well as by man, has a beautiful distinct livery, coloured by melanin and carotenoids and perhaps also by pterine.
Pterins, pigments characteristic of the wings of the butterflies, have been recognised in various species of chameleon and are probably more common in reptiles than is believed. Isoxanthopterine contributes (yellow) to the green colour of the mamba Dandroaspis viridis.
The amphibians owe their colours, sometimes even bright colours, to the carotenoids, the pterines, the melanins and the flavines, and their white colour or the white marks to guanine and other purine bases contained in the chromophores. No research has yet been made to establish whether pheomelanins are present in the integument of these animals. The green colour of the Amphibians is due to a blue schemochrome and a yellow pigment which is normally a pterine or a carotenoid.
In mammals the melanocytes together with the keratinocytes make up a very harmonious working group: the melanocytes synthesise the granules of melanin and the keratinocytes attend to their distribution and transport towards the surface. The colour of the skin can be modified by chemical or physical agents but the transformation is never rapid. In the amphibians, however, as in the Reptiles, and especially as in the less evolved animals, the coloured transformations can be very rapid. There are numerous coloured forms of the Amphibians, which can be composed aggregating granules of pigment inside the gills by the action of physical stimuli, also thanks to the increased number of pigments available when compared to the previous classes of animals.
The rapid change of colour in the amphibians is due to three types of chromatophore: melanophores, xanthophores, leucophores or iridophores. The chromatophores are part of a characteristic and distinct unit, both from a morphological and a physiological point of view. The iridophores are reflecting bodies, formed from guanine as well as from from hypoxanthine and adenine. The iridophores are made from very hard masses of platelets and it is probable that, according to the crystalline state of the purine base, the size of the crystals and their orientation, they can produce different effects, like white, iridescence or blue. In fact, if a thin section of the green skin of the frog Hyla cinera is washed with alcohol the yellow pigment is removed and the iridophores appear blue because of the Tyndall effect.
Flavins and pterins
Riboflavin has recently been identified, the pigment already encountered in the eye of the galago, in the xanthophores of the toads Bufo alarius and Scaphiopus couchi. Under the microscope (X 50) the skin of Salamandra maculusa appears black because of the presence of melanin (melanophores), yellow because of the presence of pterines (pteriphores) and white from the presence of guanine (guanophores, iridophores). Pterin can be isolated from various species of frog.
The carotenoids can be isolated from the frogs Hyla arborea, Rana esculenta, Rana temporaria, Pelobates fuscus, Alytes obstetricans, Atelopus stelzneri, Phrynomerus bifasciatus, Hyperolius marmoratus, Dendrobates tinctorius, Rana pipiens, Xenopus laevis, Hyla cinerea, Hyla arenicolor and Agalychnis dachnicolor or from the salamanders Triton cristatus, Salamandra maculosa, Salamandra salamandra and Salamandra atra.
Several carotenoids have been identified in the skin of the toads Bufo viridis, Bufo calamita, Bufo vulgaris, Bombinator ingneus, Bufo alarius and Scaphiopus couchi and in the newts Triturus Pleurodeles waltli, Taricha torosa and Diemictylus viridiscens.
Carotenoids have also been found in the eyes of the axolotl (Ambystoma mexicanum), and a sort of uredele amphibian bred in the laboratory to carry out scientific experiments ( Siredon mexicanum).
The skin of fish is often richly coloured and has compositions and patterns of a striking elegance, like for example those of tropical fish. The white and the iridescence of Fish are due to deposits of small guanine crystals, and the ventral part is particularly rich in these. The phenomenon of iridescence and the shiny effect of the birifringent crystals can be modified by changes of expansion and concentration of electro-active melanin inside the chromatophore. The blue colour of Fish can be due either to a chromoprotein or a schemochrome, the green to the effect of a schemchrome with a yellow pigment, while the dark green and the olive green come from the combination of a black and a yellow or orange chromatophore. The colouration of Fish is often in relation to their physical and psychic state or to their environments. The animals can change colouraration quickly and notably under the action of physical stimuli by a neurohormonal mechanism. In some species of Fish, often in those of the abysses, the skin has luminous organs of a glandular nature which emit light, either spontaneously or under the action of physical stimuli, and which can be switched on or off. The light may be coloured because of the presence of chromatophores on the derma which cover the generator organs of light and takes on yellow, red, blue colours with an intensity which varies, sometimes from individual to individual.
The pigments which contribute to the colouration of Fishes belong to the classes of melanins, carotenoids, pterines, flavines, bile pigments and purine or guanine bases (white).
The teleost fish Hippocampus hudsonius.
Species are red,yellow, brown, black due to carotenoids, melanin,pheomelanin.Physical colouration are see.
The clear iridophores, the melanophores, the erythrophores and the dark blue schemochrome background appear very clearly in preparation of a section of the skin of the Bermuda parrot fish Sparisoma viride and Sparisoma abildgaardi. The secret of the fascinating polychromes, both static and dynamic, of Fish lie in the relationship between the various chromatophores and in the distribution of the granules of pigments in the cytoplasm of the chromatophores. The movement of the granules of pigment, also common to other elements of the cells, remains a mysterious aspect of living material. For the Fish there are two theories:
The first considers that the, negatively charged, granules migrate electrophoretically along different potential gradients and are thus attracted or repelled by different zones of the cell, and in turn by the potentials found on the membrane which are influenced by potassium ions (external and internal concentrations of ions with respect to the membrane).
The second theory starts form the observation that under the electron microscope one sees microtubes of diameter about 500 Ň in the melanophores of some Fish, and the granules of pigment should move between these. The movement could be realised through the work of microfilaments of about 50 Ň positioned along the microtubes and able to contract under the action of hormones or other active substances.The two theories seem complementary.
All the black colourations of Fish are due to the deposition of granules of melanin in the skin. Different physical and environmental factors may influence the production of melanin. In experiments carried out in the aquarium one can, for example, show the influence of light on pigmentation in a way which recalls suntanning in man. Illumination the ventral part of some fish induces the appearance of melanin. The small tropical fish Lebistes reticulatus produces more melanin when it is raised on a dark background and contemporaneously diminishes the quantity of the guanine which makes it lighter, while total darkness causes a reduction of the melanogenesis. For Fish being black or white is very important. A white fish on a black background is easy prey for birds like seagulls, while black fish on a dark backgrounds manage to elude predators more easily.
Melanin is also found located in tumour forms, similar to the melanomas in mammals, which, interestingly, are hereditary (Platypoecilus). Often one finds flavines (riboflavin) associated to the melanins, like in eels. These pigments colour the eyes of many fish yellow.
Several yellow and red colourations can be due to pterines. These pigments are distinguished from carotenoids because they are fluorescent. The have been isolated from Carassius auratus, from Xiphophorus helleri and from Platypoecilus maculatus.
The carotenoids, especially lutein, taraxanthine and astaxanthine, as blue and red chromoprotein, or under the form of esters, contribute to the colours of fish. The pigment astaxanthine is found in the common freshwater fish Carassius auratus, in the cod Sebastes norvegicus, common in Norwegian markets, in salmon and in the red marks of trout. Carotenoids have been identified in the skin of the soles Pleuronectes flesus, Pleuronectes platessa, Pleuronectes limanda and Pleuronectes microcephalus, in the smelt Osmerus eperlanus, in the mackerel Scomber scombrus, in the salmon Salmo salar, Salmo gairdneri, Salmo fario, Salmo umbla, Oncorhyncus nerka and Cyclopterus limpus, in the shiny red fins of the pike Esox lucius, in the marine dorado Beryx dedactylus, in the red parts of the rock salmon Sebastes marinus, in the fresh water perch Perca fluviatilis, in the dark yellow of the eel Lota lota, in the Mexican fish Platypoccilus maculatus and Xiphoohorus helleri, in the Japanese carp Oryzias latipes (lutein), in the paradise fish Macropodus opercularis, in Colisia lalia, Colisia fasciata (lutein and violaxanthine), in the brown of the trout Salmo trutta (lutein and astaxanthine), in a fish of the Pacific Fundulus parvipinnis (taraxanthine), in the green fish Girella nigricans, in the Millerís thumb Gillichthys mirabilis, in the perch Cymatogaster aggregatus (taraxanthine), in the Garibaldi fish Hypsypops rubiconda (esterified taraxanthine).
Fish can also change colour with diet. The cod Gadus morrhua is generally yellowish, greenish or silver-grey but a variety on the Norwegian coast which eats small crabs rich in carotenoids is red-orange.
The carotenoids, like those of the Labrus mixtus and in the Crenilabrux parvus, play an important role in colourations which differentiate the sexes. Fish can take on wedding attire under the action of certain hormones by means of kinetic transformations of colours, as do the wrasse, the sea bream and the stickleback.
Haemoglobin - Bile pigments
Haemoglobin contributes little to the colours of Fish. The gills are red because of haemoglobin. Little is known about the role played by the porphyrins as colourants of the skin. On the contrary , derivatives of bilenone give the blue colour to the wrasse, the green and green-blue to the gar Belone belone, to Cottus scorpius and to Strongylira exilis.
The chromatic pyramid
If for a moment we stop and consider the chemical structures which contribute to the pigmentation of tissues (skin, hair, feathers, integument) of the Vertebrates we notice that their number is limited to a few fundamental types: the black melanins, the dark red or brown pheomelanins, the yellow, red and blue carotenoids, the yellow flavines, the green or blue bile pigments, the white, yellow or red pterines and the white guanine.
Distributing the various pigments for the classes of animals one can built a pyramid which leads to the thought that with the evolution of the animals from fish to mammals the number of the chemical species of the pigmented cells is ever diminishing. Naturally, wishing to attribute a particular role in evolution to the pigments, the localisation of a flavine in the eye of the galago appears more and more extraordinary and we must ask ourselves how a porphyrin could finish up in the feathers of the turaco.
In men with red hair the skin is no longer protected from solar radiation, in that it is not able to synthesise melanin, and it is presumable, also taking into account the genetic pressure of other races, much more populous and having melanocytes, that pheomelanins will no longer be present in man in the distant future.
Another distinction between man and the animals may thus be in the field of the biochromes and man can be placed alone at the apex of the pyramid.
The tunicates contain vanadium and free sulphuric acid, and are able to synthesise an animal cellulose.
The vanadium is found in the blood cells in the form of a proteic complex called haemovanidine which has a light green colour in solution and which can be seen in some transparent animals of the Ascidian family. The function of haemovanidine is not well known but does not seem to possess the properties of the so-called respiratory pigments like haemoglobin, haemocyanin, etc. Ascidiae procure metal from the sea, and a large ascidia is able to accumulate 5g of vanadium per hour, so that studies are under way to understand the filtering mechanism which these animals possess so us to use it for the practical scope of extraction of precious metals from the sea. The Tunicates also present lively red and yellow colours and red-brown colourations. Some are white or have parts coloured white. The study of these pigments is somewhat neglected, perhaps because of the difficulty of obtaining the biological material in a sufficient quantity, at least for the investigative techniques of the past. In some cases it has been ascertained that the white is due, as happens in other animals, to the presence of the guanine or uric acid (see pterines) and the yellow and red because of carotenoids.
The carotenoids (astaxanthine) have been identified in Botrillus violaceus, Amaroucium proliferum, Styela rustica, Cynthia papillosa, Microcosmus sulcatus and Dendrodoa grossularia. In some of these animals capsaxanthine, a carotenoid present in many foods has been found. It is believed, correctly, that the carotenoid is not an animal pigment but that it is occasionally found in examples which have ingested alimentary detritus thrown into the sea from ships.
Of the Ascidiae, like the Ascidia fumigata, one can extract yellow and red or red-brown pigments which can be distinguished from the carotenoids because they become black by heating or by the action of alkalis. Their nature is not known.
The colours and coloured patterns of these animals are among the most beautiful and most fantastic of the marine invertebrates. Besides being due to the pigments common to other animals, the different colourations, are also due to the presence of a new class of chemical compounds: the spinochromes and the echinochromes. These are often responsible for the intense red and the dark violet of the Echinoids. However, the biological significance of such pigments is not very clear.
One has the impression that many pigmented cells of sea urchins and of sea cucumbers are sensory elements and that the pigments, capturing specific photons, transmit their excited state to a receiver which, after analysis, correlation and integration, allows the animal to perceive and use the light for its life.The pigments then, though not directly participating in photochemical processes, can carry out a significant role of protection and filtration on the surface of the animal, and are sensible both to light and to specific wavelengths of light.
The Holothuria nigra, some varieties of tropical sea urchin Diadema, many Ophiurians and some Crinoids are black. It is probable that the pigments are melanins, although chemical analyses carried out according to methods recently developed are not available. It seems that the black pigment of Holothuria forskali, which has the properties of a melanin, is formed by the work of protozoons which have an oxidising system for transforming tyrosine into melanin, and which are found in the plasma of the animal. From a histological point of view the black pigment of Ophiocomina nigra is a melanin, in that it is contained in melanocytes of characteristic form.
Spinochromes and echinochromes
These are pigments characterised by a naphthoquinonic system. They can be isolated from the shell and the spines of the sea urchin through extraction with ether containing HCl. They colour the animal brown, red and violet. The relative quantity of spinochomes can modify the colour, as in the case of the violet and olive green spines of the Paracentrotus lividus.
Recently a new spinochrome with the following structure
has been isolated from the spines and the shell of the Salmacis sphaeroides.
Echinochromes and spinochromes have been identified in Dendraster excentricus, Pseudocentrotus depressus, Anthocidaris crassispina, Heterocentrotus mammilatus, Echinus esculentus, Diadema antillarm, Psammechinus miliaris, Strongylocentrotus purpuratus, Arbacia aequiturbeculata, Arbacia pustolosa and Arbacia punctulata.
These pigments are very common in the sea urchins, but are also found among the sea cucumbers as seen by the isolation and identification of the namakochrome in the holothuria Polycheira rufescens.
The carotenoids, among which astaxanthine, either free or linked with a protein, give beautiful yellow, orange, green, red, blue and viola colours to starfish like Solaster papposa, Henricia sanguinolenta, Asterias rubens, Solaster endeca, Astropectan californicus, Patiria minata, Pisaster giganteus, Luidia ciliaris and Astrpecten irregularis.
As well as carotenoids, one may extract small quantities of porphyrins from the starfish, as in the case of the Asterias rubens, but it is not very clear if they contribute to the colour of the animals.
The carotenoids are found in the Ophiuroids (similar to starfish). Those of not very deep water are blue, green, red and yellow while those of the abysses are orange or red like Ophioderma longicauda, Ophiocomina nigra, Ophiura texturata, Ophiopholis aculeata, Ophiotrix fragilis, Ophiopteris papillosa and Amphiura chiajei.
In sea urchins one finds carotenoids located in the gonads and in also parts of the integument. Their colours do not appear clear because they are masked by the intensely coloured echinochromes.
The Holoturoids often have dark colours which are little visible on the outside, even though carotenoids can be extracted from various parts of the body. The red colour shown by some of Psolus phantaus, Cucumaria elongata, Phyllophorus pellucidus and Stichopus termulus does not seem to be from carotenoids, and perhaps comes from are echinochromes.
In the holoturiae one also finds yellow and red pigments of an unknown structure, which blacken in an alkaline environment, similar to those of certain Tunicati. Quinones?
The pigments of the classes of the Crinoids or the sea lilies have been little investigated. These can be white, brown, green, yellow red or violet. The pigments are generally soluble in water and have the property of changing colour in acid or alkaline environments. This property recalls that of the oxyanthraquinones, which seem to be effectively present in Antedon bifida, Comatula pectinata and Comatula cratera. A mixture of pigments which have viola colourations with the alkalis can be obtained from Comatula pectinata, with a yield of 5% (on dry weight). One of these has been isolated by chromatography and possesses the structure reported in following:
The Arthropods have bodies covered by a cuticle (exoskeleton) which is mainly quite robust but constructed in such a way as to allow the animals different types of articulation. The cuticle is formed by a special polysaccharide, chitin (acetylated polymer of glucosamine), of a protein, (sclerotin), which has molecules bonded by o-dioxybenzols (the simplest is the pyrocatechol). The cuticle is rigid, but also so light as to allow the animal, as in the case of insects, to fly. The thick cuticle of the Crustaceans is relatively heavy and much more rigid, in that in it includes several calcium salts, phosphates and carbonates, both in an amorphous states and in a crystalline states. The cuticle is usually intensely coloured because of the presence of biochromes which belong to the groups of melanins, carotenoids, bile pigments, purine bases and ommochromes. The pigments are common in the cuticle, but in the case of the Crustaceons are contained in chromatophores which undergo chromatic cycles under the influence of solar illumination. The colour of the entire animal, in the case of a transparent cuticle, can also be that of the blood plasma. In some rather rare cases, the animal can appear completely red because of the presence of haemoglobin, or in other cases changes colour because the plasma is coloured by pigments of vegetable origins (chlorophyll) eaten in food. The cuticle can also be coloured by a schemochrome or present beautiful iridescence due to the phenomena of interference of light which strikes very thin lamellae of chitin superimposed and interspersed with strata of material with a contrasting refractive index.
The beetle Brachinus crepitans use unpleasantquinones to gain and secure thair habitat
This class includes about 1 million species, for which reason it is considered as the richest in forms that exists on the Earth. The number of pigments responsible for the colours in these animals is limited, even though the patterns and compositions are very varied and quite beautiful to see. Patterns and colours are very important factors in the lives and in the evolution of the insects. Many animal sexual colourations are determined by different pigments among which the melanins, the pterines and the carotinoids predominate, but schemochromes can also intervene. Individuals of one sex can have patterns coloured only by pigments while individuals of the other sex may have microscopic structures which can produce tonalities of blue because of the dispersion of light, or delicate phenomena of iridescence because of interference of light. In this way the wings of a female butterfly can appear yellow or chestnut brown because of the presence of pterines or ommochromes, while in the male they are brilliant blue because of the Tyndall effect.The tropical butterfly Heliconius erato gives preference to certain colours which must be considered at the basis of the phenomenon of courtship. If one moves pieces of cloth or of coloured card attached to thread in front of it one notes that the butterfly prefers the patterns made with orange marks on a black background, while it is not attracted by uniform colours, with the exception of red. When bees look for food for the first time are particularly attracted to blue and yellow, but this preference can change for other colours which are linked to richer sources of nectar, and such preference is maintained in a quite rigid way until the source of the food is finished. It is clear that in some way bees have the capacity of elaborating the information food-colour, behaviour which may suggest fascinating research for neurochemistry .
Many species of insects can avoid predators by using active mimetics (13) changing colour rapidly and taking on one similar to the background, or, vice versa, the pigmentation can favour the predator by making animals which would not otherwise have the chance of catching the necessary food invisible. One example of a predator favoured by pigmentation is that of the spider which, having taken on the same colour as the flower, manages to easily catch the bee searching for nectar. Another example of mimetics is offered by the Bacillus rosius which takes on colours and shapes of a twig. But other and more refined chromatic figures are necessary for insects in the pitiless fight of natural selection. Several Orthopterans imitate dead leaves and leaves with mould, some butterflies assume a livery which figures the excrement of birds or which copy a spider or other insects known to be poisonous to its predators, or show terrifying aspects with the appearance of coloured patterns on the wings which seem to be eyes. The most striking fact is that insects can have several lines of defence. The orthopteran Ommathoptera pictifolia has the colour and the aspect of a dead leaf, but if it is disturbed, besides showing its lively internal polychrome by flapping its wings it also produces coloured marks which appear like eyes and which provoke a certain confusion in the assailant. The emittero Laternaria phosphorea uses a repertoire of defensive aspects: besides perfectly mimetizing itself with the environment takes the form of a small crocodile complete with teeth and ocular prominences; if attacked it shows two large eyeshaped marks on the wings and as a last expedient covers its abdomen with a waxy substance which seems to be mould and which probably induces the predator to believe that the insect is not edible. Naturally, colours and patterns are hereditary factors in insects and their use is not the result of previous experience, as occurs in the higher animals, even though hereditary factors are influenced by the experience in the course of evolution.
The colours of the insects are under the influence of several physical factors. The stick insect Carausius morosus is green if raised at a low temperature and grey or black at a higher temperature. The desert grasshopper Schistocerca gregaria shows numerous black marks on a yellow background if it proliferates at temperatures around 40įC but these diminish or disappear completely at lower temperatures. Particular environmental conditions can modify the colourations of insects. Another example, taken from the world of the grasshoppers, (insects studied in every aspect by man because of the great damage they provoke to crops and vegetation), is the locust Locusta migratoria which, if raised in groups is black and orange while it takes on the colour of the environment if raised individually.
Insects accumulate and transform theb-carotene, contained in food, into various carotenoids like lutein, violaxanthine, taraxanthine and astaxanthine. Small quantities of other carotenoids are found in extracts of tissues, as also happens for other animals, but these do not contribute in a significant way to the colour of the animals, representing, rather, an intermediate phase in the passage of the b-carotene to various carotenoids.
The green and blue colours are due to protein-carotenoid complexes or protein-biliary pigment complexes, as well as to schemochromes, or to the combination of a biochrome with a schemochrome, as is often the case for green.These coloured complexes are a chemical mystery.
Carotenoids are responsible for the change which one sees at the beginning of the sexual maturation of locusts (Locusta migratoria). In this phase of development the males become a bright yellow colour, in that theb-carotene transfers from fatty tissues to the integument. Locusts of the genus Oedipoda have posterior wings which can be blue, red or yellow, according to whether the astaxanthine is combined with a protein or not. The green colour of these insects originates, instead, as an effect of the combination of two chromo-proteins with a carotenoid as the prostethic group (yellow) and a bile pigment (blue) as the other.
The hemipterons, an order of insects to which the common yellow and red coloured bug Perillus bioculatus also belongs, obtain carotenoids by sucking the potato beetle Leptinotarsa decemlineata which eats leaves. The ladybirds (Beetles) also obtain their yellow and orange colours from carotenoids by eating aphids which in turn take the pigment from plants.
Carotenoids are found in the elytra of the ladybirds Clythra quadripunctata, Lina populi, Lina tremulae, Coccinella septempunctata, Coccinella quinquepunctata and Melanosoma vigintipunctatum which has an elytron with twenty black marks on a yellow background.
The bug Pyrrhocoris apterus owes its red colour to the presence of lycopene which is the same carotinoid which colours the tomato red. However, generally a red colour is due to a pterine, erythropterine (14).
The dark red, orange, yellow of some bees are due to carotenoids which the insects take from pollen after having modified or accumulated it as it is. Some of these carotenoids are also found in honey, giving it its characteristic amber colour.
The green colour of the stick insect Carausius morosua is due to the combined effect ofb-carotene and the a isomer (15) with a blue pigment (mesobiliverdin), while the red marks on the femur are due to pure a-carotene. The green colour of the mantes Sphodromantis bioculata and Mantis religiosa is due to carotenoids and a blue biochrome. The green grub Sphinx ligustri, Tettigonia viridissima, Tettigonia cantans, Meconema varium, the phytophagous orthopterons Acrida turrita, Phaneroptera quadripunctata owe their colour to a carotenoid which is found mixed with a bile blue pigment. The posterior wings of the grasshoppers Oedipoda caerulescens and Oedipoda schochii contain a blue pigment soluble in water, while those of the Oedipoda miniata which are red, should owe their colour to a carotenoid and to a bile pigment combined with a protein. In other locusts, Acrotylus insubricus, Calliptamus italicus, Oedipoda aure, Oedipoda decorus, the yellow, red and blue pigments are due to carotenoids bonded with proteins. The pigments can be precipitated with ammonia sulphate and by hydrolysis give astaxanthine.
Distribution of carotenoids in Insects
Coccinella septempunctataa -carotene, b -carotene, licopene
Coccinella quinquepunctatab -carotene, cantaxanthine
Clytra quadripunctatab -carotene
Lina populib -carotene
Lina tremulaeb -carotene
Melanosoma vigintipunctatuma -carotene, b -carotene
Bombyx morib -carotene, lutein
Perillus bioculatusb -carotene
Carausius morususa -carotene, b -carotene, ketocarotenoide
Locusta migratoriab -carotene, astaxanthine
Oedipoda decorus carotenoprotein
Oedipoda miniatab -carotene
Oedipoda schochii carotenoprotein
Schistocerca gragaricab -carotene, astaxanthine
Tettigonia viridissimab -carotene, cryptoxanthine, lutein
Mantis religiosa carotenoprotein
Lutein,violaxanthine and taraxanthine have been identified in the silkworm Bombyx mori.
One can isolatea and b-carotene and lycopene from the ladybird Coccinella septempunctata, by chromatography on allumina.
The green which can be observed in the moth Procris statices is a schemochrome, while the emerald green of the moth Geometrinae or the silver green of the Bena prasinana of the Cymbiadae family are biochromes which have not been studied in depth. The green pigments of the magnificent oleander hawk-moth Daphis nerii and of the plant bug Psylla mali are still unknown.
Just as a cloth tissue with threads of yellow and black appears olive-green, the interleaving of the yellow (carotenoids and pterins) and black (melanins) scales in the posterior wings of the butterflies Euckloe cardamines and Pontia daplidice produce an olive-green colour.
Many of the black colourations of the insects are due to melanins, but given the particular nature of these pigments it is difficult to determine differences of structural type with the black colouration of the other animals. The melanin in the cuticle is difficult to analyse, in that it is not found in granules but is diffused and mixed, if not actually bonded with the sclerotin and the chitin. A melanin which is easier to study is that present in the so-called tumours of the fly Drosophila melanogaster and which forms starting from tyrosine, like that of other animals. Melanin is also present in different phases of development of the larvae. The capsule of the egg of beetle starts white but then becomes brown and finally becomes black. In the course of development of the larvae of some insects light can provoke strange variations of colour. Illuminating the larvae of Pieris brassicae, Vanessa io, or Vanessa urticae with blue of violet light one has abundant production of melanin, while using yellow light the synthesis of melanin is quite modest.
In the Insects one can see red-brown or brown colourations which are generally attributed to the ommochromes, but it is not to be excluded that such colourations may instead be given by melanins and pheomelanins. Melanin has the function of protecting the tissue under the action of very intense light and ultraviolet radiation, besides it contributes to the hardness of the cuticle and avoids the desiccation of the organism associated with exposure to radiation.
The porphyrins (electrochromophores) do not accumulate in the insects in such a way as to contribute to their colour. The biliary pigments which derive from the porphyrins, instead, colour the cuticle and the wings of the animals.
The wings of the diurnal butterfly Pieridi contain small quantities of a bile pigment in a complex with a green coloured protein. Washing on a million samples has isolated mesobiliverdine in the crystalline state. Therefore, in this case we have a different green which originates in the combined action of a biochrome with a schemochrome or by two biochromes of different colours. It is very probable that bile pigments are responsible for the blue colour of the posterior wings of the grasshopper Oedipoda coerulescens, frequent in places exposed to the sun.
The midge Chironomus, similar to a mosquito is known in the countryside around Rome because it sucks human blood. When it is born it is green because of biliverdin which accumulates together with bilirubin in the fatty tissue of the larva. One can isolate a blue pigment soluble in water from the wings of the butterflies Pteria brassicae, Pteria napi, Gonepterix rhamni, Catopsilia rurina and Catopsilia statira, this gives a biliary pigment by hydrolysis.
Essentially the chromophore of chlorophyll differs from the porphyrins by having two additional hydrogen atoms, located on positions 7 and 8. This brings about the interruption of the conjugation of double bonds and as an effect a change of the colour from red to blue.
The passage from derivatives of chlorophyll to porphyrins, and from these to biliary pigments requires a complex series of reactions if done in the laboratory. The same transformations are, on the contrary, made very easily by the flat American bug Anasa tristis which eats green plants. Magnesium is found in its intestine and the blood. Its epidermis and other parts of its body are coloured by the pheophorbids (colourants derived from chlorophyll,), while the fatty tissue is green because of the presence of a derivative of the bilenone.
The pterins, with the bile pigments and the carotenoids, contribute to the red, yellow and brown colours of the wings of butterflies. White, the silvery aspect, and the phenomenon of iridescence are due to the pterines together with guanine and uric acid. The black colour is instead due to melanins (black pterines ? )..
Pterines are also found in the eyes of some insects (Drosophila) and in the integument of the Hymenoptera, to which common flies, like Vespa crabo, Vespa germanica and Vespa vulgaris belong.
The pterines take different names which indicate the source or the colour or the chemical structure: guanopterine, leucopterine (white), xanthopterine (yellow), erythropterine (red), chrisopterine, mesopterine, isoxanthopterine, sepiapterine, pterine, 6-pterincarboxylic acid, pterorodine, 7,8-dihydroxyxanthopterine.
The fundamental nucleus of the pterines originate from the system:
of the purine (2-oxypurine) by the enlargement of the pentatomic ring a with the glyossal which provides the carbon atom necessary. The purine system would, in turn, be constructed with carbons deriving from formic acid and nitrogens from different aminoacids (16).
The pterines are insoluble in organic solvents (ether, ligroin benzene, etc.), more or less soluble in water, but easily soluble in acids and alkalis. They are generally difficult to crystallise and one needs to start from thousands of animals in order to isolate them. From a thousand Pieris brassicae one obtains 0.1-0.2 g of leucopterin; from a thousand Gonepteryx rhamni 0.3-0.6 g of xanthopterin. Pterins are not present in plants.
The haemolymph of the Aphids, vulgarly called plant lice and greenfly, contain a yellow pigment soluble in water called protoaphine. The protoaphine can be transformed into an intensely coloured pigments by enzymatic oxidation, among these are xanthaphine, which should be responsible for the colouration of the Aphids.
The Aphis fabae which feeds on the Vicia faba, a plant in which dopa is present, appears black, but the colouration is not due to melanin but to the intense colour of the aphine (17).
These are pigments which, because of some of their properties, have sometimes been mistakenly identified as melanins. The ommochromes are often brown but can also be yellow, red and viola. They are similar to some pheomelanins because of their solubility in HCOOH, alkalis and mineral acids. They give a violet colour with H2SO4, and some reversible changes of colour both with oxidants and with reducents. Their name derives from the fact that they were found in the eye (from greek omma = eye). They divide into ommatins, with a low molecular weight and soluble in alkalis, and in ommines, with a high molecular weight and stable to alkalis. It is easy to recognise them: if one cuts the head of about twenty blowflies Calliphora erythrocephala and soaks them with a little methyl alcohol acidified by hydrochloric acid one obtains a yellow solution. Adding a little of potassium hydroboride one has a red colouration due to the formation of the reduced form of xanthommatin.
The ommochromes are not localised only in the eyes of insects as was once believed. In the chromatophores of some stick insects (Dixippus) one finds a brown ommatin which makes the colouration of the tegument more or less dark by concentrating or diluting in the cells. Rodommatine and ommatine D are found in the wings of the niphelid Alglais urticae. In the butterflies Papilio xuthus and Papilius dardanus kinurenine, a precursor of the ommochromes, is present in the wings, and suggests there are ommochromes as well as pterines.
Ommochromes are also found in the locusts and their quantity varies, as also occurs for the melanins, according to whether the insects are in a solitary phase or in a group. Among the Odonates the ommatines are responsible for the brown-red colouration of the dragonflies. In the genus Sympetrum the red and yellow-brown colours which distinguish the males from the females seem to be products from ommatines in differing stages of oxidation. The ommatine is sometimes found in a thin later with the function of making the Tyndall effect more evident, as happens for some dragonflies of a beautiful metallic blue colour.
In the Coccidian insects anthraquinonie derivatives like carminic acid (I), kermesic acid (II) and laccaic acid are present.
Carminic acid is the main pigment of the ladybirds. It is found in the dried bodies of the female of the Mexican insect Dactylopius coccus, which feeds on cactus. More precisely it is located in the globules, in the eggs and in the adipose tissue and can represent 50% of the dry weight of the body. It is almost absent in males. Carminic acid, or a pigment strictly correlated to it, has also been found in other South-American species including the D. confus, D. tomentosus and D indicus, and probably in the European species Porphyrophora polonicus.
Kermesic acid is the main component of kermes, and is the oldest known colourant. It is obtained from the female of the Kermococcus ilicis, which feeds on the Mediterranean oak (kermes oak), and is in particular of the Quercus coccifera.
Lac is a complex mixture secreted by the females of various Coccidae insects in India and in South-East Asia, in a particular way by Techardia lacca and Coccus laccae. Laccaic acid is a red hydro-soluble pigment present in lac. Its structure is not known, but is similar to that of carminic and kermesic acids. The biogenesis of these pigments is not known.
The carotenoids are very common in Crustaceans. The red, blue and green colourations are due to astaxanthine (Astacus, type of lobster) in a free state, or esterified or combined with proteins. In general a blue colour indicates astaxanthine combined with a protein. The carotene-protein complex can be formed through the oxygens with reactive groups of the protein or through a activated double link of the linear chain of the carotenoid with the protein, with a mechanism which is not yet clear.
The proteic complex splits under the action of temperature and the astaxanthine is freed, this transforms into an intensely red coloured compound called astacine.
Chemically astaxanthine cuts away from the protein by alkaline saponification even using more bland temperature conditions. It can be obtained, for example, as a disodium salt from which it can be freed with acetic acid. In the pure and crystallised state astaxanthine has a blue-violet colour different to that which is seen in animals where it is, obviously, diluted. It crystallises into violet needles from benzene or pyridine.
The crustaceans, like other animals, cannot synthesise the skeleton of the carotenoids, but use theb-carotene present in nutrients as a starting product, which they modify with the introduction of oxygen , that is, by an essentially oxidative process. In fact, in the animals the b-carotene is almost always found next to partially oxidised intermediates.
The colour of the crustaceans, resulting from concentrations of pigments in the tissues and from combinations with proteins, is under the influence of several factors. Prawns change colour to adapt to the environment and can do this in less than half an hour. Intense light and high temperature can induce the prawn to change colour and in some prawns the colours vary with altitude and is very intense in the mountains. Light favours the deposition of the carotenoids in tissues, in fact the back of the crab or the lobster is more exposed and is much more coloured. When the crab Carcinus moenas nears the period of reproduction it becomes green or orange red. In the same crab there are visible white marks which disappear with maturation. Since white is almost always due to deposition of purinic bases (guanine, uric acid, leucopterine) in the tissue, and since, realistically, the bases come from the nucleic acid (rich in purines) in the diet one can deduce that the young crab, unlike the adult, prefers a food rich in nucleic acids. For the females of the prawn Palaemon serratus the appearance of a line of white marks under the abdomen signifies that they are ready for mating and also here there is, perhaps, the sign of an active metabolism of nucleic acids.
The dark green colouration of the amphipod (suborder of the Arthrostracea crustaceans) Gammarus chevreuxi is due to a carotenoid-protein complex, while the eyes are coloured by ommochromes. In the red eye of a mutant so so the brown ommochromes are absent, replaced by carotenoids or dark ommochromes (ommines). The carotenoids impart their characteristic colouration to numerous species of decapod crustaceans like Homarus, Palinurus, Galathea and Carcinus. From several coloured varieties of the isopod, (suborder of the Arthrostracea), Idothea granulosa one can isolateb-carotene, echynenone, cantaxanthine, and lutein besides ommochromes. The isopod Asellus aquaticus, a cave dwelling crustacean, also contains b-carotene and other carotenoids and it is probable that, given the lack of light in the environment in which these animals live, the carotenoids taken from food are conserved in the same state without undergoing the typical oxidation. Among the small entomostracea crustaceans, which make up an important part of plankton and serve as food for fish, like the Diaptomus vulgari, one finds blue carotenoid-protein complexes.
The eyes (the cuboidal optical stratum) of the copepod Idya furcata are blue because of a carotenoid, probably in the form of a complex with a protein.
Astaxanthine has been identified, subject to isolation, from Astacus gammarus, Maja squinado, Portunus puber, Leander serratus, Potomiobus astacus, Cancer pagurus, from the pink prawn Nephrops norvegicus next to a hydrocarbon C31H64, from copepod Calanus finmarchicus, from Homarus gammarus, Hippolyte californiensis, Eupagurus prideauxii, and Lepas fascicularis, from the giant Indian fresh water prawn Palaemon carcinus, from Palinurus vulgaris, from Pandulus borealis, from the English greenish-brown fresh water prawn Astacus pallipes or from the blue or red Danish prawn Astacus astacus.
The carotenoids are not only found located in the integument of the crustaceans but also colour their eggs. Astaxanthine is always the most common pigment and that which colours, in its various combinations, the green eggs of the lobster, the bluish eggs of Anapagurus chiroacanthus, the blue-green ovaries of Pandalus borealis, the blue eggs of the barnacle Lepas fascicularis.
The green colour of the small prawn Hyppolyte varians is produced by the superposition of a yellow carotenoid with a blue carotenoid-protein.
The cladocerea Daphnia and Simocephalus are more or less red coloured because of the fact that while they are transparent, the bacterium Spirobacillus cienkowskii, rich in red carotenoids, lives on them.
We have already observed that the pigments are always found in special cells. In the lobster, instead, the pigment (astaxanthine) is, exceptionally, dissolved in the shell. For that reason the animal cannot change colour if not by abandoning the entire covering. The pigment of the prawn is normally found in the chromatophores but is not fixed and can also diffuse outside the cell. In particular when it concentrates in the centre of the chromatophore the pigment links to a protein forming a complex soluble in water, often of a blue colour, which can thus diffuse outside the cell. This is a different way of colouring compared to other animals.
The apparently monotonous colours of the prawns and the crabs are effectively from combinations of pigments of brilliant colours contained in chromatophores of different forms. The variations in colour are determined by the cytoplasmataic flow which moves the granules of pigment along fixed directions under hormonal control.
The red parts of the small crustacean Apus (triops cancriforis) are due to haemoglobin. A dark green granular pigment is also recognisable on the same animal although its structure is unknown the coloration would suggest that it is a bile pigment.
The small prawn Chirocephalus diaphanus is coloured by a biliverdine.
The parasites Rizocephalae (suborder of the Crustaceans) live on the abdomen of the Decapods, like the crab Carcinus moenas, and can provoke castration and sexual inversion in the host. Septosaccus cuenoti, Peltogaster paguri, Peltogaster curvatus, Lernaeodiscus squamiferae Perez. are coloured by biliverdine and naturally can colour the host.
Portunus trituberculatus camer real-life drawing by F.Baver (1803)
Typical red colour of deap-sea shrimps
These are found in the eyes of the Crustaceans but it seems that they can also contribute to the colouration of the integument of the animal. The dark eyes of the small prawn Crangon vulgaris are coloured by ommines which are also found in the chromatophores.
The pigments of the chromatophores of the isopod (suborder of the Arthrostracea) Asellus aquaticus is very similar to xanthommathine. After death the animal spontaneously becomes red, probably because of the action of reducing bacteria.
The red pigment of the myriapod Lepralia foliacea is not known. Also the violet pigment of the connective tissue which is observed in the young centipede Lithobius fortificatus and which resembles a haemocyanine in some chemico-physical properties has not yet been studied.
Pandinus imperator from French Guinea
The carotenoid present in the grub Thromabidium is found to be astaxantine, while 10% of the carotenoids present in Metatrnycus ulmi area-carotene the remaining portion instead has not yet been identified. The hydracarins Eylais extendens and E. hamata contain b-carotene, echynenone, cantaxanthine, astaxanthine, in both the free and in the esterified forms, lutein and another unidentified carotenoid.
Haemocyanines are present in the blood of some spiders and scorpions. They have been studied in particular in the Limulus polyphemus.
In this philum the variety of living forms is large, however there is a notable homogeneity both from a morphological and a biochemical point of view. One characteristic is the presence of haemocyanine, (a protein containing copper which is blue if oxidised), in the blood while haemoglobin is more rare. The shell is a common element of the external morphology of a large number of the molluscs. The external layer is often brightly coloured and has refined, genetically determined patterns. The internal mother-of-pearl layer which is iridescent because of an interlacing and alternance of calcarious lamellae, can give the start to pearls of varied forms and different colours as a consequence of hormonal secretions.
All the pigments so far encountered contribute to the colour, sometimes brilliant, of the Molluscs or their very rapid variations of colour, as are well known in the cases of the octopus and the squid.
Tegula reginaoff deep waters southern California.
Melanin. Eumelanin, allomelanin BCM, BSM.
A rare species of Aulica aulica. off Philippines. Colour ranges from pale orange to red. Pigments (organic ? ) unknown.
The Iredalina aurantia from deap water of Japan. Pigments unknown.
Volutoconus bednallione of the rarest shell known. Off deep waters of Australia.Pigments unknown.
Pearls are obtained from molluscs ( Pteria vulgaris, margaritifera, Martensi, californica etc. ) and cephalopods ( Nautilus )
Pearls are produced if a foreign body is introduced between the mantle and the coat ( shell). Chemical composition ( similar to mother-of-pearl ) is Calcium carbonate 91%, water 2% , organic matter 6%, Unknown 0.15%. Co, Mn, Fe are present. Pigments are poor known.
Courtesy of J.M.Patterson, Department of Biological Sciences, De Paul University, Chicago,Illinois,USA.
When, in the long evolutive story, for the primitive Molluscs, came the day in which it was decided to abandon the old and cumbersome defensive system of the shell for a more agile and more modern system many problems had to be resolved to defend the tender body from predators. In the Cephalopods, for example in the squid, the velocity was notably increased by a system of propulsion by reaction (expulsion of a jet of water by one of the cavities of the body) or, as in the octopus and in the sepia (cuttlefish) a rapid and always changing response was created using a chromatophore: granules of white, yellow, orange, red, brown and black pigment of differing sizes are deposited in layers on the skin of the animal. The yellows on the surface, the reds in the middle and the browns more in depth; from their disposition and superposition and from the marks which can change position by contraction of the skin the various chromatic effects can appear and disappear giving the sensation that the colours pulse and run along the body of the animal.
The black and white zebra-like stripes of the sepia which swims among mobile algae, like shrubs in the wind, make the form of the animal incomprehensible and for this reason not recognisable. The rapid change of colour from black to white, when the danger is near, gives the impression to the predator that the animal has disappeared. If the danger persists, as a last resort the sepia emits a large black cloud made of a colloidal suspension of melanin. We may say that the sepia reacts with a different chromatic technique for every particular situation. Probably, different colourations and patterns in the Cephalopods are interpreted by the predator as powerful defensive arms and the trick, as in ancient and recent wars fought by man, often works.
Abraliopsisa pelagic cepahalopode
In the Cephalopods the pigment is contained in spherical sacks surrounded by strips of muscular fibre which, when they contract, compress the sack which then takes on a very thin flat form and occupies a surface 100 times greater than the spherical form. The variations of the form of the sack happen in a time frame of less than half a second and allow the animal to show its marks and patterns rapidly and to produce continuous variations of colouration. All this is under a complex and rigorous control operated by the central nervous system, that is, the small muscular fibres which provoke the changes of colouration of the skin compressing the sack are linked, by nerve fibre, directly to the brain or more precisely to the lobes of the subaesopheagal gangli. This situation, even though the organisation of the set of the nerve fibres seems different, is common in the octopus, the sepia and the squid.
According to the light signal which reaches the optical receptors (eyes) the animals send very precise indications of the colours and the patterns that the skin must take on to the motors (muscular fibres) of the numerous and different chromatophores. The brain is, in other words, able to elaborate the optical message.
Porphyrins colour the shell of the gastropod Chanculus pharaoni. Uroporphyrin-III is the pigment of the shell of the bivalves Venus fasciata and Pteria macroptera. Uroporphyrin-I is found in the integument of the snails Arion rufus, Arion emipiricoum, in the sea hare Aplysia, akea and in the bivalve Solecurtus. It is interesting to note, from a biogenetic view, that the red pigment which the sea hares emit with a defensive purpose is considered, by some, a derivative of bilenone. The black colour of the skin of the snails, like that of Arion ater, is not due to a porphyrin but rather to a melanin.
A very common porphyrine in the shells of Molluscs is the concoporphyrin which has a very similar structure to porphyrin-III. Both concoporphyrin and uroporphyrin-I are found in Pteria radiata, Pteria vulgaris and Pteria margaritifera. Uroporphyrin-I can be easily obtained by chromatography on talc of an acid solution in which the shells have been digested, and eluting the flourescent zone with acetone.
The various colourations of the pearl are due to free porphyrins or porphyrins in combination with metals (green pearls) and more rarely bile pigments.
The mollusc Tivella stultorum, much appreciated by gourmets of California, owes its colour to haemoglobin.
The bile pigments colour the shell of the gastropods Turbo green, and Haliotis blue.
From the Turbo regenfussi one can isolate a blue pigment which, both physically and for its chemical properties, is very similar to the glaucobiline, a derivative of bilenone.
The fresh water ostracode Heterocypris incongruens accumulates a bile pigment only when it feeds on blue or green algae. The gills of certain oysters, like the Ostrea edulis, are green. Probably the oysters ingest Diatoms, like the Navicula ostrearia which has a bluish colour because of a bile pigment, and the green colour of the oyster would result from the combination of the blue pigment and a yellow present in the gills.
The red pigment of the skin of the snail Arion rufus and the orange of the sea mollusc Haliotis rufescens are derived from bilenone. A pigment which is violet in the crystalline state and structurally correlated to the bilenone can be obtained from the black mollusc Haliotis cracherodii.
Orange and violet-brown coloured ommochromes are found in the skin of the sepia, and perhaps the pigment of the oceanic gastropod Hanshin is an ommochrome.
The most lively and frequent colours of the Molluscs are due to the presence of the carotenoids, like theb-carotene, echynenone and others. In the Lamellibranch Mytilus edulis alloxanthine is present, while in Mytilus californianus the zeaxanthine together with another pigment of an acid nature, mytiloxanthina, a new carotenoid with acetylenic bonds.
Astaxanthine has been isolated in the gastropod Pleurobranchus elegans, and also found in the bivalve Lima excavata, as well as in the eggs of Pomacea caniculata.
A xanthine which presents, unlike the other carotenoids, only one ring has been isolated from the nudibranch of the Pacific coast Hopkinsia rosacea.
The mollusc Chromodoris zebra has a dark blue surface with orange coloured lateral stripes. The orange pigment is certainly a carotenoid, while the nature of the blue pigment is uncertain, probably it should be a carotenoid conjugated with a protein.
A famous dye
Particular of Vendramin family (Tiziano 1565) London National Gallery
Murex shells (23) are found most prevalent in tropical waters. The most characteristic features of Muricidae are the numerous spiny projections of their shells. The name, purple fish from latin, comes from the dye that was extracted from Murex brandaris by mediterranean peoples more than 3000 years ago. Pliny the Elder tells how the dye was discovered and made from Murex b.
In the past the colourants used to dye cloth were of natural origins, very expensive, and their use was a secret art passed down from father to son. The precious porpora (Tyrian-purple, Ancient-purple,purple or purple-red) is famous among the colourants of antiquity and according to the procedure used, dyed cloth fiery red, viola or red-black. It was used to dye Greek papyruses, Phonecian, Egyptian and Romans cloth, and still in the early Medieval to dye clothes, from which the Italian name porporati of cardinals and priests. Recalled by Homer, Aristotle and Virgil for its beauty and its high cost, it was the colourant of kings and of dignitaries.
Some gastropods, like Murex brandaris, Murex trunculus and Purpura lapillus, produce a yellowish secretion in the hypobranchial glands, which becomes red in air. Leucobase is present in the biological material, in a protected form, which, after extraction, becomes sensible to atmospheric oxygen and in time transforms into 6,6'-dibromoindaco. This compound was certainly one of the main pigments of the porpora of the ancients.
The molecule is interesting because of the presence of two atoms of bromine. It is not known how and at which stage the halogenisation comes The various tonalities which tissues with the porpora are said to have taken on can be easily explained given that the bromine atoms are not very stable and the porpora, losing them, transforms into indaco, which, as everyone knows, is blue. One way of dying with porpora, which must not be very different to that used by the ancients, is the following: one breaks the shells of Murex and extracts the animals which are washed with sea water. By heating one obtains a liquid, which can take different colours, in which the cloth is immersed to dye. Exposed to the sun, the tissue, which emanates a terrible smell, takes on a beautiful deep tint which intensifies and becomes stable in time.
The animals of this class sometimes present lively colourations and cases of iridescence. The picture of the chemical structures responsible for the colours is necessarily incomplete given that only in a limited number of Annelids have the relative pigments been isolated and adequately characterised. Melanins are certainly responsible for the grey, brown or black tones, but the yellow and red colourations have been, in the cases studied, attributed to carotenoids. The green colour is often due to biliary pigments, but some dark green tones are due to chlorocruorine, the characteristic respiratory pigment which, in some animals, takes the place of haemoglobin. Other pigments in the Annelids are porhyrins and emerytrine.When one manipulates the worm Arenicola tinctoria (= Arenicola marina) the skin of the hands becomes yellow. The young worm is pink or red because of haemoglobin but then becomes dark. It is believed that the yellow pigment contained in the worm transforms into the darker pigment in the course of an unclear oxidative process.
From a chemical point of view the pigments which colour the polychaetes Eulalia viridis and Phyllodore viridis green, and the yellow, white, red, blue pigments of the serpula Pomatoceros triqueter (where the colouration must be the result of a combination of various pigments) have not yet been well classified.
Little studied pigments of various colours, yellow, red-brown, called uranidines are found in corals, in sponges in some sea cucumbers and in some worms. They easily become brown or become black in air. They are present in the leech Haemopsis sanguisuga but not in the common leech Hirudo medicinalis.
Fantastic interpretations, the fruit of superficial research, appear from time to time on the scientific stage and keep playing their parts for many years. This is the case of the pigment of the marine worm Halla parthenopeia (Costa) which colours the animal red-orange. It was attributed the structure of 2,3-dihydro-5,6-indoquinone-2-carboxylic acid to the great joy of those who worked on the biogenesis of melanins, in that this substance, called dopachrome, can be present in the course of the transformations which tyrosinase suffers when it forms melanin . Effectively there is no relationship between the two compounds.
The pigment which colours the epithelium of the polychaete Halla parthenopeia red is of an anthraquinonic nature, 7-hydroxy-8-methoxy-6-methyl-1,2-anthraquinone. This represents the first anthraquinone encountered in nature not substituted in the 9 and 10 positions (18)
Almost certainly this pigment is also present in the epithelium of the polychaete Lumbriconeris impatiens, of the Eunicide family, commonly used as bait by Neapolitan fishermen.
Another, probably mistaken, interpretation is given of the nature of the biochrome which colours the annelid Polycelis nigra which lives in the fresh water and which sometimes appears black and sometimes pink: it is claimed that the pink pigment is a dopachrome.
The marine annelid Chaetopterus variopedatus is black because of the presence of melanin. As well as melanin one can extract a red-brown pigment which some experts claim to be a pheomelanin. Another case among the invertebrates, in which one speaks of pheomelanin, is that of the protist Coccolithus fragilis, a very simple organisms among the first appearing on Earth, which has an orange pigment belonging to the class of pheomelanins. It is difficult to say how much of this claim is true, in that only in 1962 at Naples were the structure of the pheomelanins and their biogenesis discovered.
Haemoglobin and porphyrins
Various annelids are coloured by haemoglobin, like the marine worm Thoracophelia mucronata. The haemoglobin is not intracellular but in suspension. In the common lombric the terminal anterior part is coloured by the presence of a protoporphyrin. The lombric dies in light because of the flourescence of the porphyrin. The worm Lineus longissimus owes its colour to the porhyrines. Coprotoporphyrin-III is found in the viscera of several polychaete worms, Chaetopterus, Myxicola and Owenia. It is not sure whether the marine worm Urechis caupo is coloured by porphyrines, but the eggs deposited by this animal are coloured porphyrine pink. The emerytrine, once believed to be a porphyrin, is instead a sort of haemocyanin containing iron in the place of copper. The pigment, red if oxygenated or light yellow in the absence of oxygen, contributes in part to the colour of the marine Sipunculoids Sipunculus, Phascolosoma and Priapulus and in the polychaete annelid Magelona.
The chlorocruorin pigment, similar to haemoglobin, also for its function, is found in the blood of some Annelids. It is dichromic: green in diluted solution and red in concentrated solution. The pigment contributes to the colour of animals only in the polychaete annelids Chlorhaemidae and Ampharetidae. An exceptional fact is that in the blood of the annelid Serpula there is both clorocruorin and haemoglobin; the young have more haemoglobin, while clorocrurin predominates in the old. The coloured part of the clorocruorin can be detached from the proteic part as in the case of haemoglobin. Parting from 10 kg of the worm Spirographis one can obtain 250 mg of clorocruorin in the form of methylic esters. The heme (coloured part) differs from that of haemoglobin because a -CH=CH2 group has been substituted by a -CHO group (see the formula of the protoporphyrin-IX).
Besides changing the colour of the pigment this very simple substitution also varies the affinity, compared to haemoglobin, for oxygen which is lower, while it is higher towards carbon monoxide. Was this respiratory pigment common in the past when the composition of the atmosphere was different?
The intense green of the Bonellia viridis is due to a dioxymesopyrrochlorine (derivative of chlorophyll), while analogous pigments give the green-bluish colouration to Thalassema lankesteri. In Owenia and Chaetopterus the green colours are due to pheophorbids (other derivatives of chlorophyll), as in Owenia fusiformis.
The dark green of the polychaete of the Pacific Eupolymmia heterobranchia and the polychaete Clymenella torquata is due to the mesobiliverdin ( bile pigments). The more pronounced colouration in the sexually mature polychaete Nereis diversicolor is also due to carotenoids and to biliverdine which is found in granules in the epithelial cells. The lombric Allolobophora chlorotica is green in some parts of the body because of a biliary pigment.
In the Annelids several carotenoids are present and in some cases are visible as in the nematodes (which include known parasites of man), but in general, as in the Aronicola piscatorium, they are masked by the black of the integument. The pigment cantaxanthine has been extracted from the polychaete Sabella penicillus, while astaxathine and echynenone have been found in Myxicola infudibulum and in Megalomma vesciculosum.
The colours of the Coelentrates are among the most beautiful and the most varied in the animal kingdom. It is probable that the pigments in some of these animals with a watery body have important biological functions and it is surprising that they have been studied very little.
Hydra oligactisderive the color from the food they store
The hydras, fresh water coelenterates, have several colourations often due to algae. The Chlorohydra viridissima (Hydra viridis) owes its green colour to Chlorella. Other species are infected temporarily and others owe their colour to food. The Pelmatohydra oligactis takes its pigments from nutriment made of chironomids, insects similar to mosquitoes. The Hydra circumcincta becomes more and more red-orange when it feeds on microcrustacean copepods which are red, while if it feeds on Daphnia it takes on a red-brown colour.
The sea anemone Metridium senile is coloured white, orange, red, red-brown, brown and black (acetylene-black ?) The black variety contains melanin, while the white is due to a deposit of uric acid. The other colourations are due to carotenoids in which the quantity of melanin has an influence. Numerous coloured varieties of Actinia equina of Talia felina and of the anemone of the American Pacific coast Epiactis prolifera are produced by carotenoids. In the red varieties the most common pigment is esterified astaxanthine. The colour of the anemones can be modified by algae. The Cribrina xantogrammica has brown tentacles when it is found in illuminated waters because algae grow there.
The magnificent anthozoon (anthos = fiore, zoin = animale) Cerianthus membra-naceus of lively colours contains a red pigment, perhaps a carotene acid, soluble in ammoniac water.
Many blue and viola colorations of the jellyfish are due to carotene-proteins, which become red on heating (compare with the lobster), but it has been questioned whether the violet pigments of the Rhizostoma pulmo and of the Pelagia noctiluca are carotene-proteins.
Among the siphonphores the Velella lata and the Velella spirans have blue tissue, because of an astaxanthine-protein complex.
The predator nudibranch Fiona marina is blue because it feeds on Velella ( ? ).
Carotenoids are found in the red coral Eunicella verrecusa, but not in the corals Corallium rubru and Tubipora musica. Carotenoids are present in the madrepore Cariophyllia lloydi, in the cerianthus of the lively coloured tentacles Cerianthus lloydi, in the hydrozoan Tubularia indivisa, and in the scyphozoan Lucernaria quadricornis.
Biliverdine is found in the ectoderm, at the base of the solo Actinia felina, in the green parts of Tealia felina and in Anemonia sulcata. On the skin of Sagartia parasitica = calliactis effoeta) one sees red granules which, in a thicker layer appear violet. The pigment dissolves in alcohol acidified with acetic acid and gives a series of yellow and orange colours in an acidic environment, which tend to blue and violet in alkaline solutions. It is probable that this is a bile pigment.
The blue of the Pacific coral Halipora coerulea is, instead, due to a derivative of bilenone. In the yellow-orange coral Eugorgia ample and in other alcionare corals unsaturated fatty acids with many salified double bonds with calcium and magnesium are found, as well as terpenoids and aromatic hydrocarbons.
The fluorescent yellow colour which one notes even in sunlight of some coelenterates like Parazoanthus axinellae and Epizoanthus arcenus is due to the presence of some nitrogenated pigments discovered recently.
The chromophore system (19) is made up of the tetrazocyclopentazulenic skeleton which, in the form of two isomers, is present in these pigments, while the differences are due only to the position and the number of the substitutes on the base skeleton. The scheme presents the structures of the main pigments so far isolated.
The role of biochromes in living processes
Phytochrome is a pigment found in seeds which, absorbing radiation of a specific wavelength, sets off latent complex biological systems in the seeds, provoking, that is, the development of the plant (we can imagine the seed as the engine of a car and the phytochrome as the starting motor).
A molecular mechanism due to substances which absorb light must also be at the base of numerous and delicate physiological processes in animals.
Crabs become dark during the day and light during the night, under the action of light Tunicates close their orifices, sea urchins increase ovarian and testicular activity, ambulatory pedicles in the starfish of the sea move, the tentacles of anemones accompany the course of the sun, fresh water ocupi follow the light, in birds the duration and the intensity of light influence the development of male and female gonads, the length of the day stimulates the depositing of eggs and finally colours are created in our brains because of the action of specific radiations.
Both the phytochromes and the rodopsine are chromoproteins which are differentiated by the coloured part, in that in the first, a bile pigment is bonded to the protein and in the second a pigment which is chemically correlated to the carotenoids is bonded to the protein. Both the pigments activate the biological system by changing configuration.
We have so far considered conjugated biochromes with the proteins, especially for their decorative aspect, but it is possible that some of them play an important role as initiators of metabolic chains or belong to precious biological models ( see H.Dieter-Martin, Chimia, 49, 45-69, 1995 ).Electrochromophores are the pigments of the future ( see Home page ). In this prospective one hopes to see deeper study on the configuration of the chromoproteins and the molecular mechanism with which they transmit physical impulses.
The porphyrys are divided into three classes: Demosponge, Calcisponge, Esatinellids. The sponges are nothing other than the skeletons of some species of porphyrys fixed to the rocks or on the seabed at 20-30 metres depth. They are greyish or brownish, but may also present lively yellow, orange, red, viola and black colours due to carotenoids and melanins. The colour is not always of the animal, but, as happens also for the coelenterates, mollusc gastropods, ascids, is imparted by algae which grow on it and which clearly modify their colours. This has provoked, especially in the past, a certain confusion about the true chemical nature of the pigments of porphyrys.
The red tonality of Suberites domuncula, of the sponge of the English coast Hymeniacidon sanguinerm, of Ficulina ficu and Axinella crestagalli are due to mixtures of carotenoids which are probably, in part, only intermediate products of the synthesis of astaxanthine. The common sponge Halichondria panicea appears greenish because it contains a mixture of a yellow carotenoids and a blue (caroteno-protein).
The orange colour of the Kapanes sponge Reniera japonica is due to the presence ofb-carotene and of two new carotenoids, the renieratene and the isorenieratene which are easily separable.
A characteristic of these carotenoids, compared to those so far encountered, is the presence of two aromatic rings (a, b) and the disposition of the methyls. Besides, they present an absorption spectrum very similar to that ofb -carotene and g-carotene respectively.
reneratene = renieratene
isoreneratene = isorenieratene
Since astaxanthine is missing in these sponges, which compared to renieratene is at a higher level of oxidation, this means that the animal is able to operate, unlike other marine invertebrates and other sponges, only a bland oxidation (aromatic rings) without introducing atoms of oxygen.
Protozoa are microscopic animals which are subdivided into the classes of Flagellates, Sarcodices, Sporozoa and Cilia. With these animals we arrive at the confines between the animal and the vegetable kingdoms and where, given the dimensions of the animals the colour is only seen when they appear numerous, in colonies. This is the case, for example of the marine dinoflagellate. These beings of a various and bizarre aspect which live by preference in the hot tropical seas can multiply suddenly and so rapidly as to make the water appear salmon-pink or dark brown coloured. Many of these unicellular organisms are also luminescent for which reason in the night the sea may appear like a giant, and at times unexpected, illumination to the observer.
The animals are often pigmented, but not much is known about the chemical structures and the biological role of the pigments.
Carotenoids have, however, been isolated and identified in some cases, b-carotene and oxygenated carotenoids are found in Gonyalax polyedra, in Prorocentrum micans, and in Ceratium furca and it is for this reason that the "colour" of these waters is attributed to these biochromes.
The capacity to emit light on the part of some animals is well known thanks to glow-worms, but the phenomenon is more common than is generally believed. The luminous species are in fact very numerous among the Coelenterates, Ctenophores, Crustaceans, Cephalopods and oceanic Teleosts. Luminescence is characteristic of animals which live in the depths of the oceans: in certain areas of the sea 75% of the fish dwelling below 600 m are luminescent. Generally light emission occurs in an intermittent way, both because of a spontaneous process and under the action of external stimuli. The emission of continuous light, as in the deep sea cephalopod Spirula and in some millipedes, is rarer.
In general the colour of the light is blue or green and more rarely yellow, topaz and red. The coloured effect is sometimes due to the fact that the light emitted is filtered through a pigmented membrane. There is an interesting relationship between the wavelength emitted and the sensibility of the visual organs of the animal. For example the eyes of surface fish are particularly sensible to green light while animals which live in deep water have eyes more sensible to blue light which is that most commonly emitted by the animals themselves. These fish are thus in the best condition to perceive the weak glow which comes either from their own species or from a different species.
The luminescence measured in the animals to date interests the zone of the visible spectrum, while we know nothing on the possibility of emitting ultraviolet light.
The luminescence of the larvae of the Brazilian beetle Phrixothris is particular, it has two red marks on its head and a line of green marks along its body. In the dark one normally sees only the red marks, while if the animal is disturbed the green lights "switch on". The aspect of the animal recalls that of a night train: in the English language it is commonly called the "railroad worm".
The meaning of bioluminescence is far from being completely understood, especially because of the difficulty which is presented in the study of the animals in their natural environment. However, some fixed points have been reached and some very reasonable hypotheses have been advanced. It is certain, for example, that the glow-worm and some species deep sea of fish use bioluminescence as a sexual call. The male of the glow-worm moves in the dark searching a female and emitting its characteristic glow. When the light is emitted in the proximity of a female she flashes in response. Thus a series of crossed flashes is created which allow the male to approach closer and closer to the female until finally identifying her position...
The following mechanism for explaining the light has been proposed: the impulse which arrives at nerve ends frees the acetylcholine which spreads in the photocyte liberating the luciferase enzyme from an inhibited state; thus, one has the start of the luminous reaction.
The chemistry of the bioluminescence of the glow-worm Photinus pyralis has been clarified in every smallest detail. The reaction which generates the light consists of an interaction between luciferine and catalysed ATP from the luciferase enzyme, in the presence of oxygen and magnesium ions.
The luciferine, which can be extracted from the glow worm with a yield of about 1 mg per 2000 animals, is 2-(4'-carboxy-thiazolin)-6-oxy-benzothiazol. It has also been obtained by synthesis and as long as the asymmetric carbon atom 4' has the D- configuration the product emanates light like the natural product. The luciferine can have notable importance in biological research especially for the analysis of adenosine triphosphate (ATP). Adding luciferine and luciferase to an aqueous solution of ATP one obtains the typical light which of its intensity allows the calculation of the quantity of ATP present in the solution on the basis of its intensity.
Also the luciferase enzyme has been isolated in the pure form (in long white needles) and from the first analysis is constituted by about a thousand aminoacids. However, the sequence of the aminoacids and the active site of the enzyme remain to be established.
A chemical substrate, completely different from luciferine, is found in Cypridina a small crustacean similar to the water flea which lives both in fresh water and in seawater. The marine species emits an abundant luminous secretion of a blue colour. The reaction is simpler than that of the glow-worm, in that only cypridine, the enzyme and natural oxygen intervene in the production of light. Of all the molecules of the cypridine only a part is responsible for the luminescence, specifically that made of the rings a and b. Many others luciferins are known (firefly Photinus pyralis, sea pansey Renilla reniformis, limpet Latia neritoides )
Work with luciferine and luciferase has also been able to establish that for every molecule of luciferine used exactly one quantum of light is emitted. A return of 100%. The efficiency of the animal photogenerators is striking if one thinks about the systems that man uses for producing light in which light represents only a small part of the energy transformed. Perhaps the day that our knowledge of the animal photocytes is deepened is not far away and we may pass some very economical nights in the romantic glow of biological light.
The Authors thank lively Mr. Giuseppe Ferracane for the technical assistance given.
(1a) A.Butenandt., Angew. Chem., 69, 16 (1957).
(1b) R.Dunnel., Biol. Rev., 33, 178 (1958).
(1c) L.R.Fisher, S.K.Kon, Biol. Rev., 34 1 (1959).
(1d) E.Florey, M.Fingerman, R.Fujii, R.R.Novales, J.T.Bagnara, E.MacHadley, W.J.Davis, J.M.Goldman, W.Chavin, C.L.Ralph, W.C.Quevedo, Cellular aspects of the control of colour changes, American Zoologist, vol. 9, No.2 (1969).
(1e) S.W.Fox, The origins of prebiological systems, Academic Press, New York (1965).
(1f) D.L.Fox, Animal biochromes and structural colours, Cambridge Press, Cambridge (1953).
(1g) H.M.Fox, G.Vevers, The nature of animal colours, Sidgwich and Jackson, London (1960).
(1h) T.W.Goodwin, Biol. Rev., 27, 439 (1952).
(1i) W.Montagna, F.Hu, The pigmentary system, Pergamon Press, Oxford (1967).
(1l) R.A.Morton, Fort. Chem. Org. Naturst., 14, 244 (1957).
(1m) C.Rimington, Endeavour, 14, 126 (1955).
(1n) I.Ziegler- Gunder, Biol. Rev., 31, 313 (1956).
(1o) For the many black pigment used in painting look at: F. Brunello "Arte della tintura nella storia della umanitŗ" Neri-Pozza Ed. 1-476 Vicenza 1968; R.J. Gettens, G.L. Stout "Printing materials" Dover Pub., New York 1942.
(2) Sometimes the return of sight can be slow and the cure may even be unsuccessful. One explanation can be given in molecular terms : rodopsine is much more stable than opsine and the latter remaining for a long time without its biochrome alters and ends up by provoking the degeneration of the white cell of vision which, like other cells of the nervous system, is no longer able to reproduce itself.
(3a) M.S.Blois, H.W.Brown, J.E.Maling, Free radicals in biological systems, Academic Press, New York (1961).
(3b) J.Duchon, T.B.Fitzpatrik, M.Seiji, Melanin, Year Book of Dermatology, Year Book Medical
Publishers Inc., USA (1968).
(3c) M.Gordon, Pigment cell biology, Academic Press, New York (1959).
(3d) M.Gordon, Pigment cell growth, Academic Press, New York (1953).
(3e) W.Montagna, R.A.Ellis, The biology of hair growth, Academic Press, New York (1958).
(3f) R.A.Nicolaus, Melanins, Chemistry of Natural Products - Series edited by E.Lederer, Hermann, Paris (1968).
The melanin samples obtained until now are artefacts
V.Riley, J.G.Fortner, The pigment cell molecular, biological and clinical aspects, Annals of the
New York Academy of Sciences, New York (1963).
(4) We consider the splendid diamond and common carbon coke which is used for heating. Both are made up of carbon atoms and are insoluble. Applying the methods of systematic investigation to the former, crystalline form has established that it is formed of carbon atoms which are at the centre of a tetrahedron with four other atoms at the verticies each bonded to the central atom. In the latter, amorphous form, it is made of particles for typical size and shape.Particles are constructed with oligomers of relative low molecular weight. Oligomers are radical-polarone of type of acetylene-black.Color of melanin and pheomelanin is that of the crystalline semiconductor.
Wishing to establish an approximative parallelism with the animal pigments we can say that the yellow carotenoids, the red haemoglobin, the violet echinochromes, to name a few, belong to the "diamond type", while the melanins belong to the "carbon coke type".
(5) The terms molecule and macromolecule cannot have the traditional meaning but rather those of particle, granule, etc.
(6) It is probable that some cancerogenous forms of the skin erupt because of the interaction of free radicals and the nucleic acids.
(7) Since it is not yet possible to have a clear nomenclature of these pigments on a chemical basis we keep the old definitions and classification.
(8) L.Minale, E.Fattorusso, G.Cimino, S.De Stefano, R.A.Nicolaus, Gazz. Chim. Ital., 99, 431 (1969).
R.A.Nicolaus, G.Prota, C.Santacroce, G.Scherillo, D.Sica, Gazz. Chim. Ital., 99, 323 (1969).
R.A.Nicolaus, The nature of mammalian colours, Chim. Ind., 54, 427 (1972).
G.Misuraca, R.A.Nicolaus, G.Prota, G.Ghiara, Experientia, 25, 920 (1969).
(9) A red hair can be distinguished from a black hair by heating with hydrochloric acid: in the first case the liquid does not take on a colour, while in the second case one finds a red or violet solution. The colouration which is observed in red hairs is due to the yellow-orange pigment:
(10) Colourations obtained with vegetable sugars extracted from the crucifer Isatis tinctoria.
(11) Unpublished experiments.
(12) Examining the red-brown pigments present in the feathers of pheasants, partridges, pigeons, Rhode Island or New Hampshire hens, the fur of rabbits, goats and red human hair it was found that they are entirely constituted by pheomelanins. The hairs of some brown goats and sheep contain only eumelanin while the hairs of the roe deer contain eumelanin and pheomelanin. (Gazz. Chim. Ital., 100, 452 (1970)).
(13) H.B.Cott, Adaptive colouration in animals, Methuen, London (1966).
(14) Private communication from Prof. A.Quilico, Politecnico di Milano.
(15) Different because of the position of a double bond.
(16) Like adenine, purine is formed at relatively low temperatures from a mixture of cyanhydric acid, ammonia and water, or by the action of electrical discharges in recipients containing methane, ammonia and water. Given the relationship which exists between purine and pterine one may suppose that, like the porphyrins, these pigments were also formed on Earth before material was organised into metabolic chains. Another hypothesis is the formation of organic molecules from black matter.
(17) Private communication from Lord A.Todd, Cambridge.
(18) L.Panizzi, R.A.Nicolaus, Gazz. Chim. Ital., 82, 435 (1952).
R.A.Nicolaus, Biogenesis of melanins, Ed. Idelson, Napoli (1962).
R.A.Nicolaus, L.Caglioti, Ric. Sci., 27, 113 (1957).
G.Prota, M.DíAgostino, G.Misuraca, J. Chem. Soc. (C), 1614 (1972).
(19a) L.Cariello, S.Crescenzi, G.Prota, F.Giordano, L.Mazzarella, Chem. Comm., 99, (1973)
(19b) L.Cariello, S.Crescenzi, G.Prota, S.Capasso, F.Giordano, L.Mazzarella, Tetrahedron, 30, 3281 (1974).
(19c) L.Cariello, S.Crescenzi, G.Prota, L.Zanetti., Experienta, 30, 849 (1974).
(19d) L.Cariello, S.Crescenzi, G.Prota, L.Zanetti., Tetrahedron, 30, 3611 (1974).
(19) L.Cariello, S.Crescenzi, G.Prota, L.Zanetti., Tetrahedron, 30, 4191 (1974).
(20) W.A.Little, Superconductivity at room temperature, Scientific American, 212, 21-27 (1965)
(22) B.J.R.Nicolaus, R.A.Nicolaus,Atti Accademia Pontaniana, Vol.XLV,365-385,(1996),Ed.Giannini,Napoli (1997).
(23) H.Stix, M.Stix, R.Tucker-Abbott, H.Landshoff "The Shell, Five hundred Million years of Inspired Design" H.N.Abrams, Inc., Publishers, NY 1968.
(24) J.D.Murray, Scientific American 258, 62-70, 1988.
Via Diaz 38
Thanks are due to Mrs.E.M.Dissanayake for financial support.
Revised August 2003.