Melanocytes are specialized skin cells mainly located in the basal (bottom) layer of the epidermis.
They produce and secrete melanin, the pigment that gives skin color and protects the DNA in skins cells from UV radiation. (more)
Additional locations include:
- the middle layer of the eye (the uvea)
- substantia nigra
- the inner ear
Melanin is stored in melanosomes
Melanin is a biological polymer that occurs in the skin, hair, and feathers of vertebrates, as well as in the back of the eyeball and certain regions of the brain and some glands. Melanins occur in insect cuticle and in the eyes and eyespots of most animals. Melanins also produce the black coloration in the ink of the squid and other cephalopods, and they act as protective agents in certain microscopic organisms. In humans, melanin is best known as the colouring agent that makes our skin black, brown, reddish, or yellowish.
The name 'melanin' comes from the ancient Greek melanos, meaning 'dark', and the term was probably first applied by the Swedish chemist Berzelius in 1840. Melanin has many biological functions, including colouring the skin and hairs or feathers, strengthening plant cell walls and insect cuticle, absorbing light (and so providing photoreceptor shieldlng, thermoregulation, photoprotectlon), and it is an important free radical sink.
There are three types of melanin:
- Eumelanin is the best-known form of melanin, providing primarily black colours. Eumelanin is found in the hair and skin of humans, and it colours the hair grey, black, yellow, and brown. Eumelanin exists in two forms, black eumelanin and brown eumelanin. Black melanin produces black colours when it is present in large quantities, and grey colours when it is rarer. Brown eumelanin may produce brown hair colours when it is present in abundance, but smaller anmounts produce lighter brown, or blond, hair colours. The black variant of eumelanin is commonest in people of non-European descent, whereas ethnic Europeans more often have the brown eumelanin variety.
- Phaeomelanin (= pheomelanin) produces reddish colours. In humans, phaeomelanin is more abundant in the skin of women than men, and so their skin is slightly redder. It occurs also in hair, and provides the main colouring agent in ginger hair.
- Neuromelanin is the dark pigment that produces a black colour in certain parts of the brain.
Non human melanins include:
- The ink in the cuttlefish contains another type of melanin called sepiomelanin
- The melanins in plants are called allomelanins.
- Some melanins in Fungi are the simplest of all,polyacetylene.
Chemistry of melanins
The melanins are derivatives of the amino acid tyrosine. The enzyme tyrosinase acts to change the tyrosine into DOPA (3,4-dihydroxyphenylalanine), and then into dopaquinone. The dopaquinone can be converted to leucodopachrome and then follows one of two pathways to produce eumelanins (Figure B below). Alternatively, the dopaquinone can combine with the amino acid cysteine by two pathways to produce benzothiazines and phaeomelanins Figure A below).
Molecular structure of phaeomelanin (A) and eumelanin (B). [Diagram from http://photoprotection.clinuvel.com/node/204.]
Eumelanins are insoluble, nitrogenous pigments produced by the oxidative polymerization of 5,6-dihydroxyindoles derived enzymatically from tyrosine via DOPA. Phaeomelanins are sulfur-containing, alkali-soluble, pigments produced by oxidative polymerization of cysteinyldopas via 1,4-benzothiazine intermediates. Sepiomelanin is a form of eumelanin, present in the raw ink of cephalopods as a suspension of small, dark granules in a colourless plasma. The structure is a macromolecule or probably a mixture of polyacid polymers in which the predominant chemical unit is of the indole type. Allomelanins are produced from nitrogen-free precursors.
Proteomic and bioinformatic characterization of the biogenesis and function of melanosomes. 2006
A golden age of human pigmentation genetics.
Pain and red hair females
These qualitative sex differences appeared to be relevant to analgesia from kappa-opioid receptor (165196) agonists, a drug class reported to be clinically effective only in women.
Significantly greater analgesia from the kappa-opioid pentazocine than all other groups
OMIM MC3R Mycobacterium resistance
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OMIM Opiate receptor + IL7 + TBC":http://Omim/getmap.cgi?d4898
Iperpigmentazioni cutanee- Cause