Inactivation mechanism of tyrosinase.

Soluble tyrosinase isolated from the Harding-Passey mouse melanoma was incubated with 14C-dopa and the time course of disappearance of dopa was measured by radioactivity assay at various tyrosinase concentrations. At the end of certain incubation periods, the tyrosinase activity was lost and the dopa concentration reached at stationary levels depending on the initial tyrosinase concentrations. The kinetic studies were carried out in order to analyze the relationship between the amount of tyrosinase incubated and the amount of dopa disappeared at various incubation periods. The results of the kinetic treatments indicated that inactivation of tyrosinase occurred mainly in proportion to the total concentration of tyrosinase present and the inactivation due to the binding with reaction products did not seem to play an important role in the mechanism. In other words, the inactiva-tion mechanism involved appears to be simlar to the reaction inactivation, which is known to occur in the reaction of plant tyrosinase.