melanin melanin melanin (/ˈmɛlənɪn/ (listen); from ancient greek μέλας (mélas) 'black, dark') is a broad term for a group of natural pigments found in most organisms. the melanin pigments are produced in a specialized group of cells known as melanocytes. not to be confused with melamine or melatonin. melaninone possible structure of eumelaninmaterial typeheterogeneous biopolymer micrograph of melanin pigment (light refracting granular material—center of image) in a pigmented melanoma. micrograph of the epidermis, with melanin labeled at left. there are five basic types of melanin: eumelanin, pheomelanin, neuromelanin, allomelanin and pyomelanin. the most common type is eumelanin, of which there are two types — brown eumelanin and black eumelanin. eumelanin is produced through a multistage chemical process known as melanogenesis, where the oxidation of the amino acid tyrosine is followed by polymerization. pheomelanin, which is produced when melanocytes are malfunctioning due to derivation of the gene to its recessive format is a cysteine-derivative that contains polybenzothiazine portions that are largely responsible for the red or yellow tint given to some skin or hair colors. neuromelanin is found in the brain. research has been undertaken to investigate its efficacy in treating neurodegenerative disorders such as parkinson's. allomelanin and pyomelanin are two types of nitrogen-free melanin. in the human skin, melanogenesis is initiated by exposure to uv radiation, causing the skin to darken. eumelanin is an effective absorbent of light; the pigment is able to dissipate over 99.9% of absorbed uv radiation. because of this property, eumelanin is thought to protect skin cells from uva and uvb radiation damage, reducing the risk of folate depletion and dermal degradation. exposure to uv radiation is associated with increased risk of malignant melanoma, a cancer of melanocytes (melanin cells). studies have shown a lower incidence for skin cancer in individuals with more concentrated melanin, i.e. darker skin tone. humans albinism occurs when melanocytes produce little melanin. this albino girl is from papua new guinea. in humans, melanin is the primary determinant of skin color. it is also found in hair, the pigmented tissue underlying the iris of the eye, and the stria vascularis of the inner ear. in the brain, tissues with melanin include the medulla and pigment-bearing neurons within areas of the brainstem, such as the locus coeruleus. it also occurs in the zona reticularis of the adrenal gland. the melanin in the skin is produced by melanocytes, which are found in the basal layer of the epidermis. although, in general, human beings possess a similar concentration of melanocytes in their skin, the melanocytes in some individuals and ethnic groups produce variable amounts of melanin. some humans have very little or no melanin synthesis in their bodies, a condition known as albinism. because melanin is an aggregate of smaller component molecules, there are many different types of melanin with different proportions and bonding patterns of these component molecules. both pheomelanin and eumelanin are found in human skin and hair, but eumelanin is the most abundant melanin in humans, as well as the form most likely to be deficient in albinism. eumelanin part of the structural formula of eumelanin. "(cooh)" can be cooh or h, or (more rarely) other substituents. the arrow denotes where the polymer continues. eumelanin polymers have long been thought to comprise numerous cross-linked 5,6-dihydroxyindole (dhi) and 5,6-dihydroxyindole-2-carboxylic acid (dhica) polymers. there are two types of eumelanin, which are brown eumelanin and black eumelanin. those two types of eumelanin chemically differ from each other in their pattern of polymeric bonds. a small amount of black eumelanin in the absence of other pigments causes grey hair. a small amount of brown eumelanin in the absence of other pigments causes yellow (blond) hair. the eumelanin is present in the skin and hair, etc. pheomelanin part of the structural formula of pheomelanin. "(cooh)" can be cooh or h, or (more rarely) other substituents. the arrows denote where the polymer continues. pheomelanins (or phaeomelanins) impart a range of yellowish to reddish colors. pheomelanins are particularly concentrated in the lips, nipples, glans of the penis, and vagina. when a small amount of brown eumelanin in hair (which would otherwise cause blond hair) is mixed with red pheomelanin, the result is orange hair, which is typically called "red" or "ginger" hair. pheomelanin is also present in the skin, and redheads consequently often have a more pinkish hue to their skin as well. exposure of the skin to ultraviolet light increases pheomelanin content, as it does for eumelanin; but rather than absorbing light, pheomelanin within the hair and skin reflect yellow to red light, which may increase damage from uv radiation exposure. in chemical terms, pheomelanins differ from eumelanins in that the oligomer structure incorporates benzothiazine and benzothiazole units that are produced, instead of dhi and dhica, when the amino acid l-cysteine is present. trichochromes trichochromes (formerly called trichosiderins) are pigments produced from the same metabolic pathway as the eumelanins and pheomelanins, but unlike those molecules they have low molecular weight. they occur in some red human hair. in other words pheomelanin contains sulfur which provides the yellow color while eumelanin does not contain sulfur. neuromelanin neuromelanin (nm) is a dark insoluble polymer pigment produced in specific populations of catecholaminergic neurons in the brain. humans have the largest amount of nm, which is present in lesser amounts in other primates, and totally absent in many other species. the biological function remains unknown, although human nm has been shown to efficiently bind transition metals such as iron, as well as other potentially toxic molecules. therefore, it may play crucial roles in apoptosis and the related parkinson's disease. other organisms melanins have very diverse roles and functions in various organisms. a form of melanin makes up the ink used by many cephalopods (see cephalopod ink) as a defense mechanism against predators. melanins also protect microorganisms, such as bacteria and fungi, against stresses that involve cell damage such as uv radiation from the sun and reactive oxygen species. melanin also protects against damage from high temperatures, chemical stresses (such as heavy metals and oxidizing agents), and biochemical threats (such as host defenses against invading microbes). therefore, in many pathogenic microbes (for example, in cryptococcus neoformans, a fungus) melanins appear to play important roles in virulence and pathogenicity by protecting the microbe against immune responses of its host. in invertebrates, a major aspect of the innate immune defense system against invading pathogens involves melanin. within minutes after infection, the microbe is encapsulated within melanin (melanization), and the generation of free radical byproducts during the formation of this capsule is thought to aid in killing them. some types of fungi, called radiotrophic fungi, appear to be able to use melanin as a photosynthetic pigment that enables them to capture gamma rays and harness this energy for growth. the darker feathers of birds owe their color to melanin and are less readily degraded by bacteria than unpigmented ones or those containing carotenoid pigments. feathers that contain melanin are also 39% more resistant to abrasion than those that do not because melanin granules help fill the space between the keratin strands that form feathers. pheomelanin synthesis in birds implies the consumption of cysteine, a semi‐essential amino acid that is necessary for the synthesis of the antioxidant glutathione (gsh) but that may be toxic if in excess in the diet. indeed, many carnivorous birds, which have a high protein content in their diet, exhibit pheomelanin‐based coloration. melanin is also important in mammalian pigmentation. the coat pattern of mammals is determined by the agouti gene which regulates the distribution of melanin. the mechanisms of the gene have been extensively studied in mice to provide an insight into the diversity of mammalian coat patterns. melanin in arthropods has been observed to be deposited in layers thus producing a bragg reflector of alternating refractive index. when the scale of this pattern matches the wavelength of visible light, structural coloration arises: giving a number of species an iridescent color. arachnids are one of the few groups in which melanin has not been easily detected, though researchers found data suggesting spiders do in fact produce melanin. some moth species, including the wood tiger moth, convert resources to melanin to enhance their thermoregulation. as the wood tiger moth has populations over a large range of latitudes, it has been observed that more northern populations showed higher rates of melanization. in both yellow and white male phenotypes of the wood tiger moth, individuals with more melanin had a heightened ability to trap heat but an increased predation rate due to a weaker and less effective aposematic signal. melanin protects drosophila flies and mice against dna damage from non-uv radiation. important studies in drosophila models include hopwood et al., 1985. much of our understanding of the radioprotective effects of melanin against gamma radiation come from the laboratories and research groups of irma mosse.: 1151 mosse began in radiobiology in the soviet era, was increasingly supported by government funding in the wake of the discovery of radiotrophic microbes in chernobyl, and as of 2022 continues under the belarusian institute of genetics and cytology. her most significant contribution is mosse et al., 2000 on mice: 1151 but also includes mosse et al., 1994, mosse et al., 1997, mosse et al., 1998, mosse et al., 2001, mosse et al., 2002, mosse et al., 2006, mosse et al., 2007 and mosse et al., 2008. plants chemical structure of indole-5,6-quinone melanin produced by plants are sometimes referred to as 'catechol melanins' as they can yield catechol on alkali fusion. it is commonly seen in the enzymatic browning of fruits such as bananas. chestnut shell melanin can be used as an antioxidant and coloring agent. biosynthesis involves the oxidation of indole-5,6-quinone by the tyrosinase type polyphenol oxidase from tyrosine and catecholamines leading to the formation of catechol melanin. despite this many plants contain compounds which inhibit the production of melanins. interpretation as a single monomer it is now understood that melanins do not have a single structure or stoichiometry. nonetheless, chemical databases such as pubchem include structural and empirical formulae; typically 3,8-dimethyl-2,7-dihydrobenzodiindole-4,5,9,10-tetrone. this can be thought of as a single monomer that accounts for the measured elemental composition and some properties of melanin, but is unlikely to be found in nature. solano claims that this misleading trend stems from a report of an empirical formula in 1948, but provides no other historical detail. 3,8-dimethyl-2,7-dihydrobenzodiindole-4,5,9,10-tetrone names preferred iupac name 3,8-dimethyl-2,7-dihydrobenzodiindole-4,5,9,10-tetrone identifiers cas number 8049-97-6 chemspider 4884931 y pubchem cid 6325610 properties chemical formula c18h10n2o4 molar mass 318.288 g·mol−1 density 1.6 to 1.8 g/cm3 melting point < −20 °c (−4 °f; 253 k) boiling point 450 to 550 °c (842 to 1,022 °f; 723 to 823 k) except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). infobox references biosynthetic pathways the first step of the biosynthetic pathway for both eumelanins and pheomelanins is catalysed by tyrosinase. tyrosine → dopa → dopaquinone dopaquinone can combine with cysteine by two pathways to benzothiazines and pheomelanins dopaquinone + cysteine → 5-s-cysteinyldopa → benzothiazine intermediate → pheomelanin dopaquinone + cysteine → 2-s-cysteinyldopa → benzothiazine intermediate → pheomelanin also, dopaquinone can be converted to leucodopachrome and follow two more pathways to the eumelanins dopaquinone → leucodopachrome → dopachrome → 5,6-dihydroxyindole-2-carboxylic acid → quinone → eumelanin dopaquinone → leucodopachrome → dopachrome → 5,6-dihydroxyindole → quinone → eumelanin detailed metabolic pathways can be found in the kegg database (see