A spectrophotometric assay for mammalian tyrosinase utilizing the formation of melanochrome from l-dopa

A simple spectrophotometric method for a rapid determination of tyrosinase (EC 1.14.18.1) is described. The basis of the assay is the incubation of the enzyme with l-dopa in the presence of an optimal concentration of Zn 2+ ions and the measurement of the formation of melanochrome, as indicated by the rise in absorbance at 540 nm. Final absorbance change reflects probably two activities of tyrosinase: the oxidation of dopa to dopaquinone and the conversion of 5,6-dihydroxyindole to melanochrome. Using a purified preparation from hamster melanoma, the assay was found to be more sensitive than the commonly used dopachrome assay. Comparison with some other currently available methods for assaying tyrosinase is presented and potential applications of the assay are discussed.