Inactivation mechanism of tyrosinase in mouse melanoma

Tyrosinase [EC 1.14.18.1] isolated from mouse melanoma was inactivated during the dopa-tyrosinase 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