MOLECULAR MECHANISMS FOR MAMMALIAN MELANOGENESIS - COMPARISON WITH INSECT CUTICULAR SCLEROTIZATION

Melanogenesis is an important biochemical process for the production of skin pigments which protect many animals from the danger of s radiation. The abnormalities in melanogenesis are associated with albinism, vitiligo, as well as malignant melanoma in humans. In the lower of animals viz., insects, the exoskeleton is hardened to protect their soft bodies by a process called sclerotization, which is often accompanie melanization. Recent advances in the biochemistry of sclerotization and melanization reveal remarkable similarity between these two proce The seven stages of sclerotization are: (a) enzymatic oxidation of N-acyldopamine, (b) Michael-1,4-addition reactions of N-acyldopamine quin (c) tautomerization of quinone to quinone methide, (d) Michael-1,6-addition of quinone methides, (e) tautomerization of N-acyldopamine quin methide to 1,2-dehydro-N-acyldopamine, (f) enzymatic oxidation of 1,2-dehydro-N-acyldopamine, and (g) the reactions of resultant quino compounds. Amazingly, striking similarities in the reaction sequences are found in the melanization process starting from dopa. These compari predict a central role for quinone methides as reactive intermediates during melanization. Accordingly, recent studies provide increasing evid in favor of this proposition.