Formation of Melanin
The melanins, the pigments of skin and hair are complex polymers in which a major constituent is formed from tyrosine via dihydroxy phenyl alanine (DOPA).
The formation of melanins from tyrosine, which occurs in animals, plants and certain bacteria (B. niger), is due to the action of polyphenol oxidases or tyrosinases. Tyrosinase, is a copper containing mixed function oxidase that carries out a tricky sequence.
While the melanins of human beings are derived from tyrosine through DOPA, most polyhydroxy phenyl and aminophenyl compounds having ortho or para groups can be oxidized to pigmented polymers and the type of melanin is best shown by indicating the substance from which the melanin is formed. Thus we may have dopa-melanin, adrenaline-melanin, homogentisic acid - melanin, p-phenylenediamine melanin etc.
Melanin forms a reversible oxidation - reduction system, in which the reduced form is tan and the oxidized form is black. Melanins appear in tissues as regular, spheroid granules and represent formed elements rather than precipitated aggregates. Melanins are produced in pigment - forming cells, the melanocytes, and their formation is stimulated by adrenal cortical and especially pituitary hormones.