Hydrated electron-induced inactivation of tyrosinase in aqueous solution by exposure to cobalt-60 gamma-rays. I. Cresolase activity

Tyrosinase (0.2 mg/ml of 0.1 M phosphate buffer solution, pH 6.5) which has cresolase and catecholase activities was irradiated with ⁶⁰Co gamma-rays. The cresolase activity was measured at varying radiation doses under various atmospheric conditions. Do was found to be 350 Gy in N₂-saturated solution. The OH radical has been shown to be the main species involved in radiation-induced enzyme inactivation. However, in this study, OH radical scavengers, t-BuOH and MeOH, had no effect. O₂ which acts generally as an enhancer of OH-induced enzyme inactivation also had little effect, but N₂O a e(aq)^- scavenger, and Cu⁺⁺ markedly inhibited the inactivation indicating that e(aq)^- is the main species involved in inactivating the cresolase activity, reducing Cu⁺⁺ as the active center.