Free radical activity of melanins and related substances: biochemical and pathobiochemical aspects

Human body contains a number of natural pigments-authentic melanins, soluble melanins, neuromelanins, lipofuscins-having a similar origin-oxidation and polymerization of precursor phenols, and sharing many common characteristics among which dominates their free radical activity. Related substances can be formed from exogenous compounds introduced at some occasions to the organism. The functional properties of the pigments seem to be determined by their localization, i.e. cellular or extracellular, and as regards those intracellular ones by their subcellular compartmentalization. All the intracellular pigments mentioned in this study are associated with lysosomal enzymes at some stage of their development. A special attention was paid to a neglected group of soluble melanins. It was proposed that methylation may decide about the fate of precursor molecules whether they will join the soluble melanin pool or will be excreted as melanogens. Participation of the pigments in various biochemical and pathobiochemical processes has been reviewed.