Biochemistry of melanin formation.

ELANIN PIGMENTATION has aroused the curiosity and attention of man since the beginning of recorded history. This interest stems in part from the social, protective and cosmetic significance of pigmentation. In addition, much interest has arisen concerning the possible role of melanin formation in the development of the melanoma which has been described as having the most sinister reputation of malignant tumors (I). As Ewing (2) has stated, “The variations in pigment offer a very delicate indication of the functional activity of the cells and a unique opportunity to trace the relation between the functional activity and the growth capacity of the tumor cells.” As a result, this subject has attracted the attention of workers in many fields (3), for example, the cytologist in the study of the melanin granules; the geneticist, the anthropologist and the biologist in a study of the relationship of heredity, environment and nutrition to the development of pigment; and the organic and biologic chemists in the study of the chemical mechanism underlying melanin formation. In the past quarter of a century several comprehensive reviews on the mechanism of melanin formation have appeared (~-II), but in only a few of these has there been any consideration of the biochemical aspects of this problem. No attempt was made to connect the processes of melanin formation operating in various species. Different mechanisms were proposed for humans, lower animals and plants. Investigation of the biochemistry of melanin formation in plants, insects and marine animals had shown that the enzyme tyrosinase catalyzes the oxidation of L-tyrosine to dihydroxyphenyl L-alanine (dopa) and then the oxidation of dopa to melanin.