八角莲多酚氧化酶的酶学性质

以邻苯二酚为底物，研究八角莲多酚氧化酶（polyphenol oxidase，PPO）粗提液的酶学特性。结果表明，底物邻苯二酚最适浓度为1.0 mol/L，八角莲PPO的最适pH值为7.0，最适温度为30 ℃，90 ℃高温处理10 min，八角莲PPO酶活力仅剩11.92%。PPO催化的酶促褐变反应符合米氏动力学方程，相应动力学参数Km和vmax分别为0.230 7 mol/L和769.23 U/min。抗坏血酸、甘氨酸、乙二胺四乙酸、柠檬酸对酶活性具有抑制作用，十二烷基硫酸钠表现出激活作用，亚硫酸氢钠对酶活性的抑制作用强于硫代硫酸钠，Al3+和Cu2+对酶活性具有一定的激活作用，Ca2+对酶活性有一定的抑制作用，Mg2+、Fe2+和Fe3+对酶活性影响不显著。

Enzymatic Properties of Polyphenol Oxidase from Dysosma versipellis (Hance.) M.Cheng

Enzymatic characterization of polyphenol oxidase (PPO) from the leaves of Dysosma versipellis (Hance.) M.
Cheng was investigated using catechol as the reaction substrate. The results showed that the optimal substrate was catechol
at a concentration of 1.0 mol/L, and the optimal pH and temperature for this enzyme were 7.0 and 30 ℃, respectively. The
remaining activity of PPO was 11.92% after thermal treatment at 90 ℃ for 10 min. The kinetics of PPO reaction was fit to
the Michaelis-Menten equation, with Km and vmax value of 0.230 7 mol/L and 769.23 U/min, respectively. Different inhibitory
effects on PPO among ascorbic acid, glycine, EDTA and citric acid were observed. NaHSO3 showed stronger inhibitory
effect on PPO than Na2S2O3. The PPO could be activated by Al3+, Cu2+ and SDS. Ca2+ had certain inhibitory effect on the
PPO enzyme. In contrast, Mg2+, Fe2+ and Fe3+ had no significant effect on the enzyme activity (P < 0.05).