不同葡萄品种多酚氧化酶酶学特性比较

Comparative Enzymatic Kinetics of Polyphenol Oxidase from Different Grape Varieties

以欧美种葡萄"关口"、"金手指"、"黄密"3个品种和欧亚种葡萄"泽香"、"无核白"2个品种为实验材料,比较了5个不同葡萄品种间多酚氧化酶(polyphenol oxidase,PPO)以邻苯二酚、4-甲基儿茶酚、儿茶素、咖啡酸为底物的动力学参数K_m、v_(max)/K_m值,并比较了酶的最适p H值、最适温度、热稳定性、以及抑制剂对酶活性的影响。结果表明:测定的5个品种中,欧美种葡萄和欧亚种葡萄对邻苯二酚的亲和力存在显著性差异,对4-甲基儿茶酚、儿茶素、咖啡酸的亲和力无显著性差异;欧美种葡萄和欧亚种葡萄对邻苯二酚的催化效率存在显著性差异,对4-甲基儿茶酚的催化效率无显著性差异,"关口"葡萄对儿茶素和咖啡酸的催化效率明显高于其他4个葡萄品种。焦亚硫酸盐和抗坏血酸对5种葡萄PPO活性都有强的抑制作用,焦亚硫酸盐对其他4个品种葡萄的抑制作用强于对"关口"葡萄的抑制作用;在测定的p H值和温度中,5种葡萄PPO的最适p H值和最适温度都无明显差异。

The kinetic parameters Km and vmax/Km of polyphenol oxidase （PPO） from three Franco-American hybrid grapevarieties namely “Guankou”, “Goldfinger”, “Huangmi” and two Vitis vinifera varieties i.e., Zexiang and seedless whitewere compared towards different substrates： catechol, 4-methylcatechol, catechin and caffeic acid as well as optimal pHand temperature, thermal stability, and the effect of inhibitors on PPO activity. Results showed that the affinity of PPOfrom five varieties grapes for catechol was significantly different, whereas no significant difference was observed when4-methylcatechol, catechin and caffeic acid were used as substrates. The catalytic efficiency of PPO from Franco-Americanhybrid grapes and Vitis vinifera for catechol was significantly different while no significant difference was observed when4-methylcatechol, catechin and caffeic acid were used as substrates. The catalytic efficiency of PPO from “Guankou”grapes for catechin and caffeic acid was obviously higher than that of four other varieties of grapes. Among inhibitorstested, ascorbic acid and sodium metabisulfite had stronger inhibition on PPO from all five varieties. The inhibitory effect ofsodium metabisulfite on PPO from “Guankou” grapes was weaker than on PPO from four other varieties. Optimal pH andtemperature of PPO from five varieties of grapes had no significant difference.