MAMMALIAN PIGMENTATION

T HE MECHANISM of pigmentation in the lower animals has been fairly well established. Some of the precursors of the melanin compounds have been isolated, and the enzyme tyrosinase has frequently been identified in extracts from tissues of these lower animals. In them, it is thought that the formation of melanin proceeds from the naturally occurring amino acid tyrosine and involves enzymatic catalysis, with tyrosinase as the active enzyme. Raper and Evans 1 gave a logical series of enzymatic and chemical reactions for the pigmentation mechanism. However, tyrosinase has rarely been isolated from pigmented tissues of mammals, with the result that considerable confusion exists concerning the enzyme active in mammalian pigmentation. Bloch's 2 extensive work on the pigmentary mechanism in the human being led many to favor his theory of the existence of a special oxidase (dopase)-producing melanin in human beings by action on a prepigment l