The tyrosinase assay was performed by the method of Masamoto et al. with slight modifications. First, 65ml of 2.5mM L-DOPA solution, 10m l of DMSO with or without a sample and 105m l of 0.1 M phosphate buffer (pH 6.8) were mixed. The mixture was preincubated at 25 °C for 10 min. before 20m l of 1380 units/ml tyrosinase in aqueous solution was added, and the reaction was monitored at 475 nm. A control reaction was conducted with DMSO. The O.D. values were measured by a UV spectrophotometer at 475 nm using an ELISA Microplate Reader