This article covers a biochemical approach to melanogenesis. It is divided into four parts: The first two parts are a general description of melanogenesis and the structure of the intermediates of the pathway. The two types of melanin, eumelanin and phaeomelanin, are described. The third part is devoted to the properties of tyrosinase, the main enzyme of the pathway. The last part is devoted to own our contribution to the knowledge of melanogenesis, the characterization of dopachrome tautomerase, its properties, and the role of 5,6-dihydroxyindole (DHI) versus 5,6-dihydroxyindole- 2-carboxylic acid (DHICA) in the regulation of eumelanogenesis. It is shown that the melanin biosynthesis is a complex pathway whose regulation is not as simple as was thought a few years ago. The first part of the pathway is the well-known oxidation of tyrosine to dopaquinone. Tyrosinase is the key enzyme at these stages, but the level of dopa is crucial, since the tyrosine hydroxylation greatly depends on this co-factor. Dopaquinone is the switch point to form eumelanin (absence of glutathione) or phaeomelanin (presense of this thiol compound). In the eumelanogenesis pathway, dopachrome is also an important intermediate. Although it was thought for many years that dopachrome yielded melanin through DHI, it is now well established that dopachrome tautomerase catalyzes the tautomerization of dopachrome into DHICA. This indole is much more stable than DHI, but it can also be incorporated to the melanin polymer. The regulation of the distal phase of melanogenesis should also be pointed out as a new aspect in melanogenesis control.
