INACTIVATION MECHANISM OF TYROSINASE IN MOUSE MELANOMA *

Tyrosinase [EC 1.14.18.1] isolated from mouse melanoma was inactivated during the dopatyrosinase reaction. When ascorbate was added to the reaction system, in which dopa‐quinone is immediately converted back to dopa by ascorbate thus preventing the formation of melanin, tyrosinase inactivation similarly occurred. If superoxide anions (O2–) or singlet oxygens (1O2), are generated during the reaction they can attack the enzyme protein to be inactivated. Therefore an estimate was made with scavengers for oxygen radicals and with a liquid scintillation counter but neither was detectable. Thus the inactivation involved is not due to reaction products nor oxygen radicals.