The Role of Peroxidase Vs. The Role of Tyrosinase in Enzymatic Conversion of Tyrosine to Melanin in Melanocytes, Mast Cells and Eosinophils

Autoradiographic-histochemical observations, correlated with previous histochemical and biochemical studies in our laboratory, and with studies with isolated mammalian peroxidase, have provided evidence that mammalian peroxidase can mediate the enzymatic conversion of tyrosine to melanin, in the presence of dopa as co-factor. Our studies provided no conclusive evidence that mammalian tyrosinase has significant ability to oxidize tyrosine to melanin, although they showed that this enzyme has strong dopa oxidase activity. It is suggested that peroxidase may be the enzyme initiating melanin synthesis in vivo and that tyrosinase may utilize dopa synthesized by enzymatic activity of peroxidase. Tyrosinase may therefore function primarily as a dopa oxidase, as conceived by Bloch.