槐尺蠖多酚氧化酶的纯化及酶学特征

经40%饱和度硫酸铵分级沉淀，Sephadex G-100凝胶过滤等步骤，将槐尺蠖Semiothisa cinerearia Bremer et Grey 多酚氧化酶纯化，纯化倍数为6.96倍。该酶对焦性没食子酸，邻苯二酚和L多巴的Km值分别为0.23 mmol/L, 0.48 mmol/L和0.49 mmol/L。多酚氧化酶在pH 7.0，37℃时活性最高，并在40℃以上条件下，随着保温时间的延长酶活力下降。用槲皮苷和硫脲作抑制剂对该酶活性的抑制结果表明，这两种抑制剂分别属于竞争性和非竞争性抑制剂。

Purification and characterization of polyphenol oxidase from Semiothisa cinerearia Bremer et Grey (Lepidoptera:Geometridae)

The kinetic properties of polyphenol oxidase (PPO) from Semiothisa cinerearia Bremer et Grey, a forestry insect, were studied after the enzyme was partially purified by 40% saturated (NH₄)₂SO₄ and Sephadex G-100 gel filtration. The results showed that the 6.96 fold purification was achieved from the crude enzyme. The affinities of PPO with the substrates pyrogallol, catechol and L dopamine (L DOPA) were not different significantly, and the K_m with the three substrates was 0.23 mmol/L, 0.48 mmol/L and 0.49 mmol/L, respectively. The optimum pH was 7.0 and the best temperature was 37℃ for the tested PPO. The effects of two compounds as inhibitors of the reaction catalyzed by the enzyme were also tested. Those results indicated that quercetin could inhibit the PPO activity through competitive inhibition and thiourea could also inhibit the enzyme activity but through non competitive reaction.