Inhibition of tyrosinase activity by 4-tert-butylcatechol and other depigmenting agents.

4-tert-Butylcatechol (TBC) is an antioxidant widely used in industry and a potent depigmenting agent to the skin of the workers. In this study, tyrosinase was extracted from tissue-cultured human melanoma cells and purified by polyacrylamide gel electrophoresis. T1 and T2 tyrosinase, which migrated differently on the gels, were treated with TBC as well as other depigmenting agents and natural substrates of tyrosinase. Changes in the enzyme activity on dopa oxidation were quantified by photometric and radiometric analysis. The enzyme activity was inhibited by TBC and hydroquinone, but only at a high concentration that is toxic to tissue-cultured melanocytes. The activity was also decreased by tyrosine, but was increased by dopa, particularly at a lower concentration. The results indicated that the reported methodology is useful for testing the effects of chemicals with depigmenting or pigmenting potential. TBC and hydroquinone are inhibitors of tyrosinase at concentrations higher than 1 x 10(-3) M. Dopa and tyrosine alter tyrosinase activity in the second step of melanogenesis in the same manner that has been reported to occur in the first step-conversion of tyrosine to dopa.