Hydrated electron-induced inactivation of tyrosinase in aqueous solution by exposure to cobalt-60 gamma-rays. II. Catecholase activity.
Tyrosinase (0.2 mg/ml) was irradiated with 60Co gamma-rays. The catecholase activity was measured at varying radiation doses under various atmospheric conditions. D0 was found to be 1.25 kGy and hit number to be 2 in N2-saturated solution. OH radical scavengers, t-BuOH and MeOH, had no effect. O2 which is an enhancer of OH-induced enzyme inactivation had little effect. But N2O as a e aq scavenger and Cu++ markedly protected against the inactivation indicating that e aq was the main species to inactivate the enzymatic activity. By Ultrogel chromatography, it was found that the enzymatic activity was lost when this enzyme dissociated into its subunits. Thus, it was concluded that the radiation-induced inactivation was due to the reduction of Cu++ as the active center and the chelater with e aq followed by the dissociation.
Terato
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Division of Gene Chemistry, Graduate School of Gene Science, Faculty of Sciences, Hiroshima University, Japan.
Yamamoto
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O
D000596:Amino Acids / Q000032:analysis; D001487:Basidiomycota / Q000201:enzymology; D002396:Catechols / Q000378:metabolism; D002850:Chromatography, Gel; D003037:Cobalt Radioisotopes; D003545:Cysteine / Q000494:pharmacology; D004307:Dose-Response Relationship, Radiation; D016166:Free Radical Scavengers / Q000494:pharmacology; D005720:Gamma Rays; D017665:Hydroxyl Radical; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000528:radiation effects*; D010545:Peroxides / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000494:pharmacology; D020122:tert-Butylhydroperoxide
D000596:Amino Acids; D002396:Catechols; D003037:Cobalt Radioisotopes; D016166:Free Radical Scavengers; D010545:Peroxides; D017382:Reactive Oxygen Species; D017665:Hydroxyl Radical; D020122:tert-Butylhydroperoxide; D014442:Monophenol Monooxygenase; D003545:Cysteine; C034221:catechol