Reaction of the sulfhydryl group with an oxidation product of beta-3,4-dihydroxyphenyl-L-alanine.

The sulfhydryl group plays a role in the biological formation of melanin. Mechanisms suggested for the inverse relationship between the sulfhydryl group and the formation of melanin in mammalian skin include inhibition of tyrosinase and reaction with precursors of melanin (1, 2). However, knowledge in this field is fragmentary, and definitive proof of mechanism is lacking (3). The present work is a study in vitro of the reaction between an oxidation product of p-3,4-dihydroxyphenyl-L-alanine and the sulfhydryl group of cysteine or glutathione in the presence of tyrosinase at pH 7.4.