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Melanin (; from el, μέλας ''melas'', "black, dark") is a broad term for a group of natural
pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compound , CH4; is among the simplest organic compou ...
s found in most
organism In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological ...

organism
s. Melanin is produced through a multistage chemical process known as
melanogenesis Melanocytes are melanin-producing neural-crest, neural crest-derived cell (biology), cells located in the bottom layer (the stratum basale) of the skin's epidermis (skin), epidermis, the middle layer of the human eye, eye (the uvea), the inner ear ...
, where the
oxidation Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter ...

oxidation
of the
amino acid Amino acids are organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, a ...

amino acid
tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemi ...

tyrosine
is followed by
polymerization In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer, monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks.Clayden, J ...
. The melanin pigments are produced in a specialized group of cells known as
melanocytes Melanocytes are melanin-producing neural crest-derived cells located in the bottom layer (the stratum basale The ''stratum basale'' (basal layer, sometimes referred to as ''stratum germinativum'') is the deepest layer of the five layers of the ...
. There are five basic types of melanin:
eumelanin Melanin (; from el, μέλας ''melas'', "black, dark") is a broad term for a group of natural pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at ...
,
pheomelanin Melanin (; from el, μέλας ''melas'', "black, dark") is a broad term for a group of natural pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at ...
,
neuromelanin Neuromelanin (NM) is a dark pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compound , CH4; ...
, allomelanin and pyomelanin. The most common type is eumelanin, of which there are two types— brown eumelanin and black eumelanin. Pheomelanin is a
cysteine Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the chemical formula, formula HOOC-CH-(NH2)-CH2-SH. The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. The thiol is suscepti ...

cysteine
-derivative that contains poly
benzothiazine
benzothiazine
portions that are largely responsible for the color of
red hair Red hair (also known as orange hair and ginger hair) is a hair colour found in one to two percent of the human population Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalit ...

red hair
, among other pigmentation. Neuromelanin is found in the
brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tis ...

brain
. Research has been undertaken to investigate its efficacy in treating neurodegenerative disorders such as
Parkinson's Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system The motor system is the set of central and peripheral structures in the nervous system t ...
. Allomelanin and pyomelanin are two types of nitrogen-free melanin. In the human skin, melanogenesis is initiated by exposure to
UV radiation Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that stud ...
, causing the skin to darken. Melanin is an effective absorbent of light; the pigment is able to dissipate over 99.9% of absorbed UV radiation. Because of this property, melanin is thought to protect skin cells from
UVB radiation damage
UVB radiation damage
, reducing the risk of folate depletion and dermal degradation, and it is considered that exposure to UV radiation is associated with increased risk of
malignant melanoma Melanoma, also redundantly known as malignant melanoma, is a type of skin cancer Skin cancers are cancers that arise from the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with thre ...

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 Afghan children with fair skin Human skin color ranges from the darkest brown to the lightest hues. Differences in skin color among individuals is caused by variation in pigment A pigment is a colored material that is completely or nearly i ...
. However, the relationship between skin pigmentation and
photoprotection Photoprotection is the biochemical process that helps organisms cope with molecular damage caused by sunlight Sunlight is a portion of the given off by the , in particular , , and light. On , sunlight is and through , and is obvious as ...
is still uncertain.


Humans

In humans, melanin is the primary determinant of
skin color Afghan children with fair skin Human skin color ranges from the darkest brown to the lightest hues. Differences in skin color among individuals is caused by variation in pigment A pigment is a colored material that is completely or nearly i ...
. It is also found in
hair Hair is a protein filament In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Ph ...

hair
, the pigmented tissue underlying the iris of the eye, and the
stria vascularis The upper portion of the spiral ligament (which forms the outer wall of the cochlear duct) contains numerous capillary A capillary is a small blood vessel The blood vessels are the components of the circulatory system that transport blood th ...
of the
inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear T ...

inner ear
. In the brain, tissues with melanin include the
medulla Medulla or Medullary may refer to: Science * Medulla oblongata The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is ...
and pigment-bearing neurons within areas of the
brainstem The brainstem (or brain stem) is the posterior stalk-like part of the brain A brain is an organ Organ may refer to: Biology * Organ (anatomy) An organ is a group of Tissue (biology), tissues with similar functions. Plant life and anim ...

brainstem
, such as the
locus coeruleus The locus coeruleus () (LC), also spelled locus caeruleus or locus ceruleus, is a nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom ...
. It also occurs in the
zona reticularis The zona reticularis (sometimes, reticulate zone) is the innermost layer of the adrenal cortex The adrenal cortex is the outer region and also the largest part of an adrenal gland. It is divided into three separate zones: zona glomerulosa, zona f ...
of the
adrenal gland The adrenal glands (also known as suprarenal glands) are endocrine gland Endocrine glands are ductless glands of the endocrine system The endocrine system is a messenger system comprising feedback loops of the hormones released by interna ...

adrenal gland
. The melanin in the skin is produced by
melanocyte Melanocytes are melanin Melanin (; from el, μέλας ''melas'', "black, dark") is a broad term for a group of natural pigments found in most organisms. Melanin is produced through a multistage chemical process known as melanogenesis, wher ...
s, which are found in the basal layer of the
epidermis The epidermis is the outermost of the three layers that comprise the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate Vertebrates () comprise all species of animal Animals (also calle ...
. 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 Albinism is the congenital absence of any pigmentation or colouration in a person, animal or plant, resulting in white hair, feathers, scales and skin and pink eyes in mammals, birds, reptiles, amphibians and fish and invertebrates as well. V ...
. 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

Eumelanin polymers have long been thought to comprise numerous cross-linked 5,6-dihydroxy
indole Indole is an aromatic forms of benzene (top) combine to produce an average structure (bottom) In chemistry, aromaticity is a property of cyclic compound, cyclic (ring (chemistry), ring-shaped), plane (geometry), planar (flat) structures with p ...

indole
(
DHI
DHI
) and 5,6-dihydroxyindole-2-
carboxylic acid A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with substituent, R referring to the alkyl, alkenyl, aryl, or other group. ...
(
DHICA DHICA (5,6-dihydroxyindole-2-carboxylic acid) is an intermediate in the biosynthesis Biosynthesis is a multi-step, enzyme-Catalysis, catalyzed process where substrate (chemistry), substrates are converted into more complex Product (chemistry), pro ...

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.


Pheomelanin

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. In chemical terms, pheomelanins differ from eumelanins in that the oligomer structure incorporates
benzothiazine
benzothiazine
and
benzothiazole Benzothiazole is an aromatic heterocyclic compound with the chemical formula . It is colorless, slightly viscous liquid. Although the parent compound, benzothiazole is not widely used, many of its derivatives are found in commercial products or i ...

benzothiazole
units that are produced, instead of DHI and
DHICA DHICA (5,6-dihydroxyindole-2-carboxylic acid) is an intermediate in the biosynthesis Biosynthesis is a multi-step, enzyme-Catalysis, catalyzed process where substrate (chemistry), substrates are converted into more complex Product (chemistry), pro ...

DHICA
, when the amino acid
L-cysteine Cysteine (symbol Cys or C; ) is a semiessential amino acid, essential proteinogenic amino acid with the chemical formula, formula HOOC-CH-(NH2)-CH2-SH. The thiol side chain in cysteine often participates in enzymatic reactions, as a nucleophile. ...

L-cysteine
is present.


Trichochromes

Trichochromes (formerly called trichosiderins) are pigments produced from the same
metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell (biology), cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence ...
as the eumelanins and pheomelanins, but unlike those molecules they have low molecular weight. They occur in some red human hair.


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 In chemistry, the term transition metal (or transition element) has three possible definitions: * The IUPAC definition defines a transition metal as "an chemical element, element whose atom has a partially filled Electron shell, ''d'' sub-shel ...
such as iron, as well as other potentially toxic molecules. Therefore, it may play crucial roles in
apoptosis Apoptosis (from Ancient Greek Ancient Greek includes the forms of the Greek language Greek ( el, label=Modern Greek Modern Greek (, , or , ''Kiní Neoellinikí Glóssa''), generally referred to by speakers simply as Greek (, ) ...

apoptosis
and the related
Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a chronic condition, long-term neurodegeneration, degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disea ...
.


Other organisms

Melanins have very diverse roles and functions in various organisms. A form of melanin makes up the ink used by many
cephalopod A cephalopod is any member of the mollusca Mollusca is the second-largest phylum In biology, a phylum (; plural The plural (sometimes list of glossing abbreviations, abbreviated ), in many languages, is one of the values of the gram ...
s (see
cephalopod ink Cephalopod ink is a dark-coloured or luminous ink Ink is a gel, sol, or solution Image:SaltInWaterSolutionLiquid.jpg, Making a saline water solution by dissolving Salt, table salt (sodium chloride, NaCl) in water. The salt is the solute a ...
) 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 Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that stud ...
from the sun and
reactive oxygen species Reactive oxygen species (ROS) are highly Reactivity (chemistry), reactive chemicals formed from O2. Examples of ROS include peroxides, superoxide, hydroxyl radical, singlet oxygen, and alpha-oxygen. The reduction of molecular oxygen (O2) produce ...
. Melanin also protects against damage from high temperatures, chemical stresses (such as
heavy metals upright=1.2, Crystals of osmium, a heavy metal nearly twice as dense as lead">lead.html" ;"title="osmium, a heavy metal nearly twice as dense as lead">osmium, a heavy metal nearly twice as dense as lead Heavy metals are generally defined as ...
and
oxidizing agents An oxidizing agent, also known as an oxidant or oxidizer, is a substance that has the ability to oxidize (mild reducing agent) are added to powdered potassium permanganate (strong oxidizing agent), a violent redox reaction accompanied by ...
), and biochemical threats (such as host defenses against invading microbes). Therefore, in many pathogenic microbes (for example, in ''
Cryptococcus neoformans ''Cryptococcus neoformans'' is an encapsulated yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species ...

Cryptococcus neoformans
'', a fungus) melanins appear to play important roles in
virulence Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most contexts, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host (biology), host. The Pathogen#Pathogenicity, ...
and
pathogenicity In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
by protecting the microbe against
immune In biology, immunity is the capability of multicellular organisms Multicellular organisms are organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that emb ...
responses of its
host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places *Host, Pennsylvania, a village in Berks County People *Jim Host (born 1937), American businessman *Michel Host (19 ...
. 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 A photosynthetic pigment (accessory pigment; chloroplast pigment; antenna pigment) is a biological pigment, pigment that is present in chloroplasts or photosynthetic bacterium, bacteria and captures the light energy necessary for photosynthesis. P ...
that enables them to capture
gamma rays A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, i ...
and harness this energy for growth. The darker
feather Feathers are epidermal growths that form a distinctive outer covering, or plumage Plumage ( "feather") is a layer of feather Feathers are epidermal growths that form a distinctive outer covering, or plumage, on dinosaurs, both avi ...

feather
s of
bird Birds are a group of warm-blooded vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...

bird
s owe their color to melanin and are less readily degraded by bacteria than unpigmented ones or those containing
carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organ ...
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 Keratin () is one of a family of structural fibrous proteins also known as ''scleroproteins''. Alpha-keratin Alpha-keratin, or α-keratin, is a type of keratin Keratin () is one of a family of fibrous structural proteins known as Scleroprot ...

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
mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share" or "to be i ...
ian pigmentation. The coat pattern of mammals is determined by the
agouti gene Agouti-signaling protein is a protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendr ...
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 An arthropod (, (gen. ποδός)) is an invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart ...

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 In living creatures, structural coloration is the production of colour by microscopically structured surfaces fine enough to interfere with visible light, sometimes in combination with pigments. For example, peacock tail feathers are pigmented ...
arises: giving a number of species an
iridescent Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to Gradient, gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, ...
color.
Arachnid Arachnida () is a class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytica ...

Arachnid
s 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
wood tiger moth
, convert resources to melanin in order 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 Aposematism is the advertising by an animal to potential predators that it is not worth attacking or eating. This unprofitability may consist of any defences which make the prey difficult to kill and eat, such as toxicity, venom, foul taste o ...
signal. Melanin protects ''
Drosophila ''Drosophila'' () is a genus of fly, flies, belonging to the family (biology), family Drosophilidae, whose members are often called "small fruit flies" or (less frequently) pomace flies, vinegar flies, or wine flies, a reference to the character ...

Drosophila
'' flies and
mice A mouse, plural mice, is a small mammal Mammals (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ...
against DNA damage from non-UV radiation. Important studies in Drosophila models include Hopwood et al 1985.


Plants

Melanin produced by plants are sometimes referred to as 'catechol melanins' as they can yield
catechol Catechol ( or ), also known as pyrocatechol or 1,2-dihydroxybenzene, is a toxic organic compound with the molecular formula C6H4(OH)2. It is the ''ortho'' isomer In chemistry Chemistry is the scientific discipline involved with Chemical e ...

catechol
on alkali fusion. It is commonly seen in the
enzymatic browning Browning is the process of food turning brown due to the chemical reactions that take place within. The process of browning is one of the chemical reactions that take place in food chemistry and represents an interesting research topic regarding ...
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 Polyphenol oxidase (PPO; also polyphenol oxidase i, chloroplastic), an enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are ca ...
from
tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemi ...

tyrosine
and
catecholamines (noradrenaline) Image:Adrenalin - Adrenaline.svg">140px, epinephrine (adrenaline) A catecholamine (; abbreviated CA) is a monoamine neurotransmitter, an organic compound that has a catechol">organic_compound.html" ;"title="monoamine neurotra ...
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-dihydrobenzo ,2,3-''cd'':4,5,6-''c''′''d''′iindole-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.


Biosynthetic pathways

The first step of the biosynthetic pathway for both eumelanins and pheomelanins is
catalysed that utilizes a low-temperature oxidation catalyst to convert carbon monoxide to less toxic carbon dioxide at room temperature. It can also remove formaldehyde from the air. Catalysis () is the process of increasing the reaction rate, rate of a ...

catalysed
by
tyrosinase Tyrosinase is an oxidaseAn oxidase is an enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), sub ...
. :
Tyrosine -Tyrosine or tyrosine (symbol Tyr or Y) or 4-hydroxyphenylalanine is one of the 20 standard amino acid Amino acids are organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemi ...

Tyrosine
DOPA
DOPA
dopaquinone
dopaquinone
Dopaquinone can combine with
cysteine Cysteine (symbol Cys or C; ) is a semiessential proteinogenic amino acid with the chemical formula, formula HOOC-CH-(NH2)-CH2-SH. The thiol side chain in cysteine often participates in enzymatic reactions as a nucleophile. The thiol is suscepti ...

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 Dopachrome is a cyclization product of L-DOPA -DOPA, also known as levodopa and -3,4-dihydroxyphenylalanine, is an amino acid that is made and used as part of the normal biology Biology is the natural science that studies life and living ...

dopachrome
→ 5,6-dihydroxyindole-2-carboxylic acid → quinone → eumelanin :Dopaquinone → leucodopachrome → dopachrome → 5,6-dihydroxyindole →
quinone The quinones are a class of organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties ...

quinone
→ eumelanin Detailed metabolic pathways can be found in the
KEGG KEGG (Kyoto Encyclopedia of Genes and Genomes) is a collection of databases dealing with genomes, biological pathways, disease A disease is a particular abnormal condition that negatively affects the structure or function of all or par ...
database (see
External links An internal link is a type of hyperlink on a web page to another page or resource, such as an image or document, on the same website or domain name, domain. Hyperlinks are considered either "external" or "internal" depending on their target or de ...
). File:L-Tyrosin phys.svg, L-tyrosine File:3,4-Dihydroxy-L-phenylalanin (Levodopa).svg, L-DOPA File:L-Dopachinon.svg, L-dopaquinone File:L-Leucodopachrom.svg, L-leucodopachrome File:L-Dopachrom.svg, L-dopachrome


Microscopic appearance

Melanin is brown, non-refractile, and finely granular with individual granules having a diameter of less than 800 nanometers. This differentiates melanin from common blood breakdown pigments, which are larger, chunky, and refractile, and range in color from green to yellow or red-brown. In heavily pigmented lesions, dense aggregates of melanin can obscure histologic detail. A dilute solution of
potassium permanganate Potassium permanganate is an inorganic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, proper ...

potassium permanganate
is an effective melanin bleach.


Genetic disorders and disease states

There are approximately nine types of
oculocutaneous albinism Oculocutaneous albinism is a form of albinism involving the human eye, eyes (''wikt:oculo-#Prefix, oculo-''), the human skin, skin (''-wikt:cutaneous#Adjective, cutaneous''), and the hair. Overall, an estimated 1 in 20,000 people worldwide are bo ...
, which is mostly an autosomal recessive disorder. Certain ethnicities have higher incidences of different forms. For example, the most common type, called oculocutaneous albinism type 2 (OCA2), is especially frequent among people of black
Africa Africa is the world's second-largest and second-most populous continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', ...

Africa
n descent and white
Europe Europe is a continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of scienc ...

Europe
ans. People with OCA2 usually have fair skin, but are often not as pale as OCA1. They have pale blonde to golden, strawberry blonde, or even brown hair, and most commonly blue eyes. 98.7–100% of modern Europeans are carriers of the derived allele SLC24A5, a known cause of nonsyndromic oculocutaneous albinism. It is an autosomal recessive disorder characterized by a
congenital A birth defect, also known as a congenital disorder, is a condition present at birth Birth is the act or process of bearing or bringing forth offspring, also referred to in technical contexts as parturition. In mammals, the process is initiate ...
reduction or absence of melanin pigment in the skin, hair, and eyes. The estimated frequency of OCA2 among
African-American African Americans (also referred to as Black Americans or Afro-Americans) are an ethnic group An ethnic group or ethnicity is a grouping of people A people is any plurality of person A person (plural people or persons) is a being t ...
s is 1 in 10,000, which contrasts with a frequency of 1 in 36,000 in white Americans. In some African nations, the frequency of the disorder is even higher, ranging from 1 in 2,000 to 1 in 5,000. Another form of Albinism, the "yellow oculocutaneous albinism", appears to be more prevalent among the
Amish The Amish (; pdc, Amisch; german: Amische) are a group of traditionalist Christian church fellowships with Swiss German Swiss German (Standard German Standard High German (SHG), less precisely Standard German or High German (not to ...

Amish
, who are of primarily
Swiss Swiss may refer to: * the adjectival form of Switzerland , french: Suisse(sse), it, svizzero/svizzera or , rm, Svizzer/Svizra , government_type = Federalism, Federal semi-direct democracy under an assembly-independent Directorial ...

Swiss
and
German German(s) may refer to: Common uses * of or related to Germany * Germans, Germanic ethnic group, citizens of Germany or people of German ancestry * For citizens of Germany, see also German nationality law * German language The German la ...

German
ancestry. People with this IB variant of the disorder commonly have white hair and skin at birth, but rapidly develop normal skin pigmentation in infancy. Ocular albinism affects not only eye pigmentation but visual acuity, as well. People with albinism typically test poorly, within the 20/60 to 20/400 range. In addition, two forms of albinism, with approximately 1 in 2,700 most prevalent among people of Puerto Rican origin, are associated with mortality beyond melanoma-related deaths. The connection between albinism and
deafness Deafness has varying definitions in cultural and medical contexts. In medical contexts, the meaning of deafness is hearing loss Hearing loss is a partial or total inability to hear Hearing, or auditory perception, is the ability ...
is well known, though poorly understood. In his 1859 treatise ''
On the Origin of Species ''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life''),The book's full original title was ''On the Origin of Species by Me ...
'',
Charles Darwin Charles Robert Darwin (; ; 12 February 1809 – 19 April 1882) was an English naturalist Natural history is a domain of inquiry involving organism In biology, an organism () is any organic, life, living system that fu ...

Charles Darwin
observed that "cats which are entirely white and have blue eyes are generally deaf". In humans, hypopigmentation and deafness occur together in the rare Waardenburg's syndrome, predominantly observed among the
Hopi The Hopi are a Native Americans in the United States, Native American tribe who primarily live on the Hopi Reservation in northeastern Arizona. As of the United States Census, 2010, 2010 census, there are 19,338 Hopi in the United States. The Ho ...

Hopi
in
North America North America is a continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as continen ...

North America
. The incidence of albinism in Hopi Indians has been estimated as approximately 1 in 200 individuals. Similar patterns of albinism and deafness have been found in other mammals, including dogs and rodents. However, a lack of melanin ''per se'' does not appear to be directly responsible for deafness associated with hypopigmentation, as most individuals lacking the enzymes required to synthesize melanin have normal auditory function. Instead, the absence of
melanocytes Melanocytes are melanin-producing neural crest-derived cells located in the bottom layer (the stratum basale The ''stratum basale'' (basal layer, sometimes referred to as ''stratum germinativum'') is the deepest layer of the five layers of the ...
in the stria vascularis of the inner ear results in
cochlea The cochlea is the part of the inner ear Inner Ear (established in 2007 in Bodø, Norway) is a Norwegian record label initiated and led by the brothers and jazz musicians Tore Johansen and Roger Johansen (musician), Roger Johansen. They opene ...

cochlea
r impairment, though why this is, is not fully understood. In Parkinson's disease, a disorder that affects neuromotor functioning, there is decreased neuromelanin in the substantia nigra and locus coeruleus as a consequence of specific dropping out of dopaminergic and noradrenergic pigmented neurons. This results in diminished
dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical , CH4; is among the simplest organic compounds. In chemistry Chemistry is t ...

dopamine
and
norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and ...

norepinephrine
synthesis. While no correlation between race and the level of neuromelanin in the substantia nigra has been reported, the significantly lower incidence of Parkinson's in blacks than in whites has "promptsome to suggest that cutaneous melanin might somehow serve to protect the neuromelanin in substantia nigra from external toxins." In addition to melanin deficiency, the molecular weight of the melanin polymer may be decreased by various factors such as oxidative stress, exposure to light, perturbation in its association with melanosomal
matrix protein Viral matrix proteins are structural proteins linking the viral envelope 250px, Schematic of a Cytomegalovirus, coat = envelope A viral envelope is the outermost layer of many types of virus A virus is a submicroscopic infectious agent ...
s, changes in , or in local concentrations of metal ions. A decreased molecular weight or a decrease in the degree of polymerization of ocular melanin has been proposed to turn the normally anti-oxidant polymer into a
pro-oxidantPro-oxidants are chemicals that induce oxidative stress, either by generating reactive oxygen species Reactive oxygen species (ROS) are highly reactive chemical molecules formed due to the electron receptivity of O2. Examples of ROS include peroxi ...
. In its pro-oxidant state, melanin has been suggested to be involved in the causation and progression of
macular degeneration Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which may result in blurred vision, blurred or vision loss, no vision in the center of the visual field. Early on there are often no sympto ...
and
melanoma Melanoma, also redundantly known as malignant melanoma, is a type of skin cancer that develops from the Biological pigment, pigment-producing cells known as melanocytes. Melanomas typically occur in the skin, but may rarely occur in the mouth, i ...

melanoma
.
Rasagiline Rasagiline (Azilect, Azipron) is an irreversible inhibitor of monoamine oxidase-B used as a monotherapy Combination therapy or polytherapy is therapy A therapy or medical treatment (often abbreviated tx, Tx, or Tx) is the attempted remediation ...

Rasagiline
, an important monotherapy drug in Parkinson's disease, has melanin binding properties, and melanoma tumor reducing properties. Higher eumelanin levels also can be a disadvantage, however, beyond a higher disposition toward vitamin D deficiency. Dark skin is a complicating factor in the laser removal of
port-wine stain A port-wine stain (''nevus flammeus'') is a discoloration of the human skin caused by a vascular anomaly (a capillary malformation in the skin). They are so named for their coloration, which is similar in color to port wine, a fortified wine, fo ...
s. Effective in treating white skin, in general, lasers are less successful in removing port-wine stains in people of Asian or African descent. Higher concentrations of melanin in darker-skinned individuals simply diffuse and absorb the laser radiation, inhibiting light absorption by the targeted tissue. In a similar manner, melanin can complicate laser treatment of other dermatological conditions in people with darker skin.
Freckles Freckles are clusters of concentrated melaninized cells which are most easily visible on people with a fair complexion. Freckles do not have an increased number of the melanin-producing cells, or melanocytes, but instead have melanocytes th ...

Freckles
and
mole Mole (or Molé) may refer to: Animals * Mole (animal) or "true mole", mammals in the family Talpidae, found in Eurasia and North America * Golden moles, southern African mammals in the family Chrysochloridae, similar to but unrelated to Talpidae ...
s are formed where there is a localized concentration of melanin in the skin. They are highly associated with pale skin.
Nicotine Nicotine is a naturally produced alkaloid Alkaloids are a class of basic BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming language In computer science Computer sci ...

Nicotine
has an affinity for melanin-containing tissues because of its precursor function in melanin synthesis or its irreversible binding of melanin. This has been suggested to underlie the increased and lower
smoking cessation Smoking cessation, usually called quitting smoking or stopping smoking, is the process of discontinuing tobacco smoking Tobacco smoking is the practice of burning tobacco village in Xanthi, Greece Tobacco is the common name of sever ...
rates in darker pigmented individuals.


Human adaptation


Physiology

Melanocytes insert granules of melanin into specialized cellular
vesicles Vesicle may refer to: ; In cellular biology or chemistry * Vesicle (biology and chemistry), a supramolecular assembly of lipid molecules, like a cell membrane * Synaptic vesicle ; In human embryology * Vesicle (embryology), bulge-like features of ...
called
melanosome Fish and frog melanophores are cells that can change colour by dispersing or aggregating pigment-containing melanosomes. A melanosome is an organelle In cell biology, an organelle is a specialized subunit, usually within a cell (biology), cell, ...
s. These are then transferred into the
keratinocyte Keratinocytes are the primary type of Cell (biology), cell found in the epidermis (skin), epidermis, the outermost layer of the skin. In humans, they constitute 90% of epidermal skin cells. Basal cells in the stratum basale, basal layer (''st ...
cells of the human
epidermis The epidermis is the outermost of the three layers that comprise the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate Vertebrates () comprise all species of animal Animals (also calle ...
. The melanosomes in each recipient cell accumulate atop the
cell nucleus In cell biology, the nucleus (pl. ''nuclei''; from Latin or , meaning ''kernel'' or ''seed'') is a biological membrane#Function, membrane-bound organelle found in eukaryote, eukaryotic cell (biology), cells. Eukaryotes usually have a single n ...

cell nucleus
, where they protect the nuclear
DNA Deoxyribonucleic acid (; DNA) is a molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical ...

DNA
from mutations caused by the
ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of s or s that have sufficient to s or s by detaching s from them. The particles generally travel at a speed that is greater than 1% of , and the electromagnetic w ...
of the sun's
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, ...

ultraviolet
rays. In general, people whose ancestors lived for long periods in the regions of the globe near the
equator The Equator is a circle of latitude, about in circumference, that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the N ...

equator
have larger quantities of eumelanin in their skins. This makes their skins brown or black and protects them against high levels of exposure to the sun, which more frequently result in
melanoma Melanoma, also redundantly known as malignant melanoma, is a type of skin cancer that develops from the Biological pigment, pigment-producing cells known as melanocytes. Melanomas typically occur in the skin, but may rarely occur in the mouth, i ...

melanoma
s in lighter-skinned people. Not all the effects of pigmentation are advantageous. Pigmentation increases the heat load in hot climates, and dark-skinned people absorb 30% more heat from sunlight than do very light-skinned people, although this factor may be offset by more profuse sweating. In cold climates dark skin entails more heat loss by radiation. Pigmentation also hinders synthesis of
vitamin D Vitamin D is a group of fat-soluble secosteroid 250px, The parent steroid skeleton. The B-ring of the parent steroid is broken between C9 and C10 to yield D vitamins. A secosteroid () is a type of steroid , hypothetical a steroid with ...
, so that in areas of poor nutrition darker skinned children are more liable to
rickets Rickets is a condition that results in weak or soft bones in children. Symptoms include bowed legs, stunted growth, bone pain, large forehead, and trouble sleeping. Complications may include bone fractures, muscle spasms, or an scoliosis, abnorm ...

rickets
than lighter skinned children. Since pigmentation appears to be not entirely advantageous to life in the tropics, other hypotheses about its biological significance have been advanced, for example a secondary phenomenon induced by adaptation to parasites and tropical diseases.


Evolutionary origins

Early humans ''Homo'' () is the genus that emerged in the (otherwise extinct) genus '' Australopithecus'' that encompasses the extant species ''Homo sapiens Humans (''Homo sapiens'') are the most populous and widespread species of primates, characte ...
evolved to have dark skin color around 1.2 million years ago, as an adaptation to a loss of body hair that increased the effects of UV radiation. Before the development of hairlessness, early humans had reasonably light skin underneath their fur, similar to that found in other
primate A primate ( ) (from Latin , from 'prime, first rank') is a eutherian mammal constituting the Taxonomy (biology), taxonomic order (biology), order Primates (). Primates arose 85–55 million years ago first from small Terrestrial animal, ...

primate
s. The most recent scientific evidence indicates that
anatomically modern humans Early modern human (EMH) or anatomically modern human (AMH) are terms used to distinguish ''Homo sapiens'' (the only extant Hominina species) that are Human anatomy, anatomically consistent with the Human variability, range of phenotypes seen i ...
evolved in
Africa Africa is the world's second-largest and second-most populous continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', ...

Africa
between 200,000 and 100,000 years, and then populated the rest of the world through one migration between 80,000 and 50,000 years ago, in some areas
interbreeding In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechani ...
with certain
archaic human A number of varieties of ''Homo ''Homo'' () is the that emerged in the (otherwise extinct) genus ' that encompasses the extant species ' (), plus several extinct species classified as either to or closely related to modern humans (dependin ...
species (
Neanderthals Neanderthals (, also Neandertals, ''Homo neanderthalensis'' or ''Homo sapiens neanderthalensis'') are an extinct species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of an org ...
,
Denisovans The Denisovans or Denisova hominins ) are an extinct Extinction is the termination of a kind of organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system ...
, and possibly others). It seems likely that the first modern humans had relatively large numbers of eumelanin-producing melanocytes, producing darker skin similar to the indigenous people of Africa today. As some of these original people migrated and settled in areas of
Asia Asia () is Earth's largest and most populous continent, located primarily in the Eastern Hemisphere, Eastern and Northern Hemisphere, Northern Hemisphere of the Earth, Hemispheres. It shares the continental landmass of Eurasia with the cont ...

Asia
and
Europe Europe is a continent A continent is any of several large landmass A landmass, or land mass, is a large region In geography Geography (from Greek: , ''geographia'', literally "earth description") is a field of scienc ...

Europe
, the selective pressure for eumelanin production decreased in climates where radiation from the sun was less intense. This eventually produced the current range of human skin color. Of the two common gene variants known to be associated with pale human skin, ''
Mc1r The melanocortin 1 receptor (MC1R), also known as melanocyte-stimulating hormone receptor (MSHR), melanin-activating peptide receptor, or melanotropin receptor, is a G protein–coupled receptor G protein-coupled receptors (GPCRs), also known a ...
'' does not appear to have undergone positive selection, while ''
SLC24A5 SLC may refer to: Places * Salt Lake City Salt Lake City (often shortened to Salt Lake and abbreviated as SLC) is the capital Capital most commonly refers to: * Capital letter Letter case (or just case) is the distinction between t ...
'' has undergone positive selection.


Effects

As with peoples having migrated northward, those with light skin migrating toward the equator acclimatize to the much stronger solar radiation. Nature selects for less melanin when ultraviolet radiation is weak. Most people's skin darkens when exposed to UV light, giving them more protection when it is needed. This is the physiological purpose of
sun tanning Sun tanning or simply tanning is the process whereby Human skin color, skin color is darkened or tanned. It is most often a result of exposure to ultraviolet radiation, ultraviolet (UV) radiation from sunlight or from artificial sources, such ...

sun tanning
. Dark-skinned people, who produce more skin-protecting eumelanin, have a greater protection against
sunburn Sunburn is a form of radiation burn A radiation burn is a damage to the skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. ...

sunburn
and the development of melanoma, a potentially deadly form of skin cancer, as well as other health problems related to exposure to strong
solar radiation Solar irradiance is the power Power typically refers to: * Power (physics) In physics, power is the amount of energy transferred or converted per unit time. In the International System of Units, the unit of power is the watt, equal to one j ...
, including the
photodegradationPhotodegradation is the alteration of materials by light. Typically, the term refers to the combined action of sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultrav ...
of certain
vitamin A vitamin is an organic molecule , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...
s such as
riboflavin Riboflavin, also known as vitamin B2, is a vitamin A vitamin is an organic molecule , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemi ...

riboflavin
s,
carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ (anatomy), organ Chemistry * Organ ...
s,
tocopherol Tocopherols (; TCP) are a class of organic chemical compounds (more precisely, various methylated In the chemical sciences, methylation denotes the addition of a methyl group on a substrate, or the substitution of an atom (or group) by a methyl g ...
, and
folate Folate, also known as vitamin B9 and folacin, is one of the B vitamins. Manufactured folic acid, which is converted into folate by the body, is used as a dietary supplement and in food fortification as it is more stable during processing and ...
. Some Northwestern Europeans have substantially lost the ability to tan as a result of relaxed natural selection. Their skin burns and peels rather than tans. This is due to the fact that they produce a defective form of a skin protein Mc1r (melanocortin-1 receptor) which is necessary for the production of melanin. They are at a distinct disadvantage in tropical and subtropical environments. Not only do they suffer the discomfort of readily burning, but they are at a much higher risk for skin cancer; the same is true of albinos. Melanin in the eyes, in the iris and
choroid The choroid, also known as the choroidea or choroid coat, is the Blood vessel, vascular layer of the eye, containing connective tissues, and lying between the retina and the sclera. The human choroid is thickest at the far extreme rear of the ey ...
, helps protect them from
ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, ...

ultraviolet
and high-frequency visible light; people with are more at risk of sun-related eye problems. Further, the ocular lens yellows with age, providing added protection. However, the lens also becomes more rigid with age, losing most of its accommodation—the ability to change shape to focus from far to near—a detriment due probably to
protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendrew in 1958, for which they received a No ...

protein
crosslinking caused by UV exposure. Recent research suggests that melanin may serve a protective role other than photoprotection. Melanin is able to effectively
chelate Chelation is a type of bonding of ions An ion () is a particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object to which can be ascrib ...
metal ions through its carboxylate and phenolic hydroxyl groups, in many cases much more efficiently than the powerful chelating ligand ethylenediaminetetraacetate (EDTA). Thus, it may serve to sequester potentially toxic metal ions, protecting the rest of the cell. This hypothesis is supported by the fact that the loss of neuromelanin observed in Parkinson's disease is accompanied by an increase in iron levels in the brain.


Physical properties and technological applications

Evidence exists in support of a highly cross-linked
heteropolymer A copolymer is a polymer A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecul ...
bound
covalently A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms. These electron pairs are known as shared pairs or bonding pairs, and the stable balance of attractive and repulsive forces between atoms, when they s ...
to matrix scaffolding melanoproteins. It has been proposed that the ability of melanin to act as an
antioxidant Antioxidants are compounds Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above ...

antioxidant
is directly proportional to its degree of polymerization or
molecular weight A molecule is an electrically Electricity is the set of physical phenomena associated with the presence and motion Image:Leaving Yongsan Station.jpg, 300px, Motion involves a change in position In physics, motion is the phenomenon ...
. Suboptimal conditions for the effective polymerization of melanin
monomer In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in th ...

monomer
s may lead to formation of lower-molecular-weight, pro-oxidant melanin that has been implicated in the causation and progression of
macular degeneration Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which may result in blurred vision, blurred or vision loss, no vision in the center of the visual field. Early on there are often no sympto ...
and
melanoma Melanoma, also redundantly known as malignant melanoma, is a type of skin cancer that develops from the Biological pigment, pigment-producing cells known as melanocytes. Melanomas typically occur in the skin, but may rarely occur in the mouth, i ...

melanoma
.
Signaling pathway In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanisms, ...
s that upregulate melanization in the
retinal pigment epithelium The pigmented layer of retina or retinal pigment epithelium (RPE) is the pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Gene ...
(RPE) also may be implicated in the downregulation of rod outer segment
phagocytosis Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis Endocytosis is a cellular process i ...

phagocytosis
by the RPE. This phenomenon has been attributed in part to foveal sparing in
macular degeneration Macular degeneration, also known as age-related macular degeneration (AMD or ARMD), is a medical condition which may result in blurred vision, blurred or vision loss, no vision in the center of the visual field. Early on there are often no sympto ...
.


See also

*
Albino Albinism is the congenital absence of any pigmentation or colouration in a person, animal or plant, resulting in white hair, feathers, scales and skin and pink eyes in mammals, birds, reptiles, amphibians and fish and invertebrates as well. V ...
*
Albinism in biology Albinism is the congenital absence of any pigmentation or colouration in a person, animal or plant, resulting in white hair, feathers, scales and skin and pink eyes in mammals, birds, reptiles, amphibians and fish and invertebrates as well. Va ...
*
Ferulic acid Ferulic acid is a hydroxycinnamic acid, an organic compound. It is an abundant phenolic phytochemical found in plant cell walls, covalently bonded as side chains to molecules such as arabinoxylans. As a component of lignin, ferulic acid is a pre ...
*
Griscelli syndrome Griscelli syndrome is a rare autosomal recessive disorder characterized by albinism (hypopigmentation) with immunodeficiency, that usually causes death by early childhood. Researchers have developed three different classifications of the form of dis ...
, a syndrome characterised by hypopigmentation *
Human skin color Human skin color ranges from the darkest brown to the lightest hues. Differences in skin color among individuals is caused by variation in pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, ...
* Melanin theory *
Melanism The term melanism refers to black pigment and is derived from the gr, μελανός. Melanism is the increased development of the dark-colored pigment A pigment is a colored material that is completely or nearly insoluble in water. In contr ...
*
Melanogenesis Melanocytes are melanin-producing neural-crest, neural crest-derived cell (biology), cells located in the bottom layer (the stratum basale) of the skin's epidermis (skin), epidermis, the middle layer of the human eye, eye (the uvea), the inner ear ...
, melanin production * Risks and benefits of sun exposure *
Skin whitening Skin whitening, also known as skin lightening and skin bleaching, is the practice of using chemical substances in an attempt to lighten the skin or provide an even skin color by reducing the melanin concentration in the skin. Several chemicals h ...
*
Vitamin D Vitamin D is a group of fat-soluble secosteroid 250px, The parent steroid skeleton. The B-ring of the parent steroid is broken between C9 and C10 to yield D vitamins. A secosteroid () is a type of steroid , hypothetical a steroid with ...


References


External links

* * * {{Authority control Skin pigmentation Skin anatomy Hair color