Melanins

Literature References: Pigments responsible for the dark color of skin, hair, feathers, fur, insect cuticle, soil; found also in fungi, bacteria, and pathological human urine where it is an indication of melanotic tumors. Structures are highly irregular polymers produced in the form of granules which may be bound to protein material. Allomelanins are found in the plant kingdom and are produced from nitrogen-free precursors. See: aspergillin, humic acid. Eumelanins and phaeomelanins are found in the animal kingdom. Eumelanins are black or brown, insoluble, nitrogenous pigments produced by the oxidative polymerization of 5,6-dihydroxyindoles derived enzymatically from tyrosine via dopa. One of the best characterized is sepiomelanin, q.v. Phaeomelanins are sulfur-containing, alkali-soluble, yellow to reddish-brown pigments produced by oxidative polymerization of cysteinyldopas via 1,4-benzothiazine intermediates. Biosynthesis from tyrosine: H. S. Raper, Physiol. Rev. 8, 245 (1928); H. S. Mason, J. Biol. Chem. 172, 83 (1948). In vitro prepn from dopa: L. E. Arnow, Science 87, 308 (1938). Series of articles on structure and biosynthesis: M. Piattelli, R. A. Nicolaus, Tetrahedron 15, 66 (1961); M. Piattelli et al., ibid. 18, 941 (1962); eidem, ibid. 19, 2061 (1963); R. A. Nicolaus et al., ibid. 20, 1163 (1964). NMR-study: G. A. Duff et al., Biochemistry 27, 7112 (1988). Determn of eumelanin metabolites in human urine: S. Pavel, W. van der Slik, J. Chromatogr. 375, 392 (1986). Review of biosynthesis: J. M. Pawelek, A. M. Körner, Am. Sci. 70, 136-145 (1982); of photochemistry and photobiology: M. R. Chedekel, Photochem. Photobiol. 35, 881-885 (1982); M. R. Chedekel, L. Zeise, Lipids 23, 587-591 (1988). Reviews: R. A. Nicolaus, Melanins (Hermann, Paris, 1968); G. Prota, Med. Res. Rev. 8, 525-556 (1988).