多酚氧化酶（PPO）催化茶多酚氧化为茶色素的反应是形成红茶品质的关键基础。茶鲜叶PPO主要以低比活的膜结合态多酚氧化酶（mPPO）存在，在红茶加工中激活为高比活的游离态（sPPO）对提高红茶品质具有重要意义。然而，目前mPPO的激活机制尚不明确。因此，本项目拟对茶鲜叶中mPPO与sPPO各组分进行纯化与质谱鉴定，通过酶学性质、分子量和蛋白序列分析，明确各组分间存在的对应关系及其在红茶加工中的变化规律；通过切割位点特异性和酶活相关性分析，结合体外酶切研究，明确参与mPPO激活作用的内源性蛋白酶及其作用顺序，探明红茶加工中mPPO的激活方式；研究mPPO在激活过程中一级和二级结构、蛋白构象、催化中心微观结构的变化，并分析对其催化特性的影响，阐明mPPO激活的分子结构转变机制。本项目将完善茶树PPO的酶学信息，并为高品质红茶的加工提供新思路。

Polyphenol oxidase (PPO) catalyzes the oxidation of tea polyphenols to tea pigment, which is the key basis on which the black tea quality develops. The membrane-bound PPO (mPPO) of low specific enzyme activity is the dominant state that it exists in the fresh tea leaves. Activation of mPPO to a soluble state (sPPO) greatly increases its catalysis activity, which is of great significance for improving the quality of black tea. However, the activation mechanism of mPPO transforming to sPPO is not yet clear. Therefore, in this project, the components of mPPO and sPPO in fresh tea leaves will be purified and identified by using mass spectrometry. Through the analysis of enzymatic properties, molecular weight and protein sequence, the relationship between the components and their transformation pattern in black tea processing will be clarified. The endogenous proteases that involves in mPPO activation and their sequence of action will be determined through the correlation analysis of cleavage site specificity and enzyme activity, combining in vitro enzyme digestion studies, to explore the activation mode of mPPO in black tea processing. The changes of primary and secondary structure, protein conformation, and catalytic center microstructure of mPPO in activation process will be investigated, and their effects on its catalytic characteristics will be analyzed to uncover the molecular structure transformation mechanism of mPPO activation. This research will contribute to complete the enzymatic information of PPO from Camellia sinensis, and provide new insights into processing of black tea of high quality.