Tyrosine Peptides as Precursors of Melanin in Mammals

Abstract

THE important role of mammalian tyrosinase in the formation of melanin has been convincingly demonstrated¹. In all earlier studies, tyrosine has been thought to be the only effective substrate, with the exception of tyrosine ethyl ester which was found by Lerner et al.² to be oxidized by Harding–Passey melanoma tyrosinase preparations. In a few cases, tyrosine peptides have been investigated as potential substrates, and Bloch³ found that human skin extracts could not oxidize glycyl-dihydroxyphenyl-alanine, while Kertész⁴ reported that glycyl-L-tyrosine was not oxidized by tyrosinase preparations obtained from human melanomas. Lerner¹ predicted that tyrosine peptides in which tyrosine occupies the N-terminal position would be substrates of mammalian tyrosinase, but that tyrosine peptides in which tyrosine occupied the C-terminal position would not.