Peroxidase, "Protyrosinase, " and the Multiple Forms of Tyrosinase in Mice1

Mammalian tyrosinase as currently defined has two catalytic functions: 1) the oxidation of tyrosine to L-3,4-dihydroxyphenylalanine (dopa) and 2) the oxidation of dopa to dopa quinone (1-9). Although an imposing body of evidence has been advanced in support of this interpretation, Okun and associates have recently chal-lenged the prevailing concept of the action of tyrosinase ( 10, 11). They have pro-posed that within mammalian melanocytes, the oxidation of tyrosine to dopa is mediated by peroxidase whereas the oxidation of dopa to dopa quinone is regulated by dopa oxidase. In their view it is the coupling of peroxidase and dopa oxidase which accounts for "tyrosinase " activity in mammals; i.e., a tyrosinase with cata-lytic action directed toward both tyrosine and dopa does not exist. Our previous studies have demonstrated that polyacrylamide gel electrophero-grams of supernatant fractions from homogenates of mammalian pigmented hair bulbs reveal the presence of multiple molecular forms of tyrosinase (12, 13). Ex-tensive examination of hair bulbs from various coat-color mutants of the mouse indicate that the multiple molecular forms of tyrosinase are under genetic contro