Sun Jian, Shi John, Zhao Mouming, Xue Sophia Jun, Ren Jiaoyan, Jiang Yueming
South China Botanical Garden, The Chinese Academy of Sciences, 510650 Guangzhou, China; Guelph Food Research Center, Agriculture and Agri-Food Canada, Guelph, Canada N1G 5C9.
Guelph Food Research Center, Agriculture and Agri-Food Canada, Guelph, Canada N1G 5C9.
Food Chem. 2008 Jun 1;108(3):818-23. doi: 10.1016/j.foodchem.2007.11.036. Epub 2007 Nov 23.
Lychee polyphenoloxidase (PPO) was extracted and partially purified using ammonium sulphate precipitation and dialysis. The comparative analysis of PPO property was performed using its endogenous substrate (-)-epicatechin and exogenous substrate catechol. The pH optima for activity and activation temperature profiles of lychee PPO were very different when the enzyme reacted with endogenous and exogenous substrates. The addition of ethylenediaminetetraacetic acid disodium salt into the endogenous or exogenous substrate-enzyme system exhibited the same lowest inhibition of the PPO activity. However, l-cysteine was most effective in inhibiting enzymatic activity in the endogenous substrate-enzyme system while ascorbic acid was the best inhibitor in the exogenous substrate-enzyme system. Fe(2+) greatly accelerated the enzymatic reaction between endogenous substrate and PPO, but Cu(2+) exerted the same effect on the reaction between exogenous substrate and PPO. Based on the kinetic analysis, lychee PPO could strongly bind endogenous substrate but it possessed a higher catalytic efficiency to exogenous substrate.
采用硫酸铵沉淀和透析法提取并部分纯化了荔枝多酚氧化酶（PPO）。使用其内源底物（-）-表儿茶素和外源底物儿茶酚对PPO的性质进行了比较分析。当该酶与内源和外源底物反应时，荔枝PPO的最适pH活性和活化温度曲线有很大差异。在内源或外源底物-酶体系中添加乙二胺四乙酸二钠盐对PPO活性的抑制作用最低。然而，L-半胱氨酸对内源底物-酶体系中的酶活性抑制最有效，而抗坏血酸是外源底物-酶体系中最好的抑制剂。Fe(2+)极大地加速了内源底物与PPO之间的酶促反应，但Cu(2+)对外源底物与PPO之间的反应有相同的作用。基于动力学分析，荔枝PPO能与内源底物强烈结合，但对外源底物具有更高的催化效率。
