Abstract:The polyphenol oxidase（PPO）from Macrocybe gigantea was investigated. The crude extracts of PPO from M. gigantea were prepared with different buffer solutions and at different pH values. Then，with catechol as the substrate，the PPO activity was measured under different substrate dosages，temperatures，pH values，inhibitors，and metal ions. And，the Michaelis constant of the enzyme was determined. The results showed that the relative activity of PPO was the highest in the crude extract prepared with phosphate buffer at pH6.8.The optimum substrate dosage，pH，and reaction temperature of PPO were 1.5 mL，6.5，and 30 ℃，respectively.The enzyme was unstable at above 30 ℃，with the relative activity of only 19.67% at 80 ℃，and it was stable at pH6-7. The inhibitory effects of inhibitors on the relative activity of PPO were in a descending order of ascorbic acid，citric acid，and ethylenediaminetetraacetic acid disodium salt. When the concentration of ascorbic acid was 1 000 mmol/L，PPO was completely inactivated. Among the metal ions，only Fe2+ increased the relative activity of PPO，and the others inhibited the relative activity of PPO. In addition，the Michaelis equation was determined with different concentrations of catechol，and the Michaelis constant of PPO was obtained to be 0.114 mol/L.