MAMMALIAN TYROSINASE: PREPARATION AND PROPERTIES

The enzyme tyrosinase, which catalyzes the aerobic oxidation of tyrosine to produce the pigment melanin, is found widely distributed in nature.Much has been reported (1, 2) on tyrosinase obtained from plant, insect, and marine animal sources, but relatively little is known concerning mammalian tyrosinase.Some years ago, Bloch and his coworkers proposed, on the basis of histochemical evidence, that melanin formation in mammalian skin was attributable to the presence of a specific enzyme whose substrate was not tyrosine but dihydroxyphenyl-n-alanine (dopa) (3).This enzyme was given the name "dopa oxidase."Largely as the result of this work, which has been amply confirmed, the concept has arisen that the primary amino acid precursor of mammalian melanin is not tyrosine but dopa, and there has even been some question as to the actual existence of a mammalian tyrosinase, although it is generally agreed that the enzyme from other sources is a true tyrosinase.In 1903 Gessard (4) found that extracts from a horse melanoma were able to catalyze the conversion of tyrosine to melanin.This was confirmed by de Coulon in 1920 (5).In 1907 Alsberg (6) prepared an extract from a human melanoma which could catalyze the formation of black pigment from catechol and possibly from tyrosine.In the following year Neuberg (7) showed that dilute extracts from a human melanoma accelerated pigment formation from tyramine and adrenalin but not from tyrosine.Recently Hogeboom and Adams (8) demonstrated that extracts from the Harding-Passey mouse melanoma possess both tyrosinase and dopa oxidase activity.They reported the separation of these two activities by ammonium sulfate precipitation.Similar results were reported by Green-