中文摘要：

研究马铃薯的PPO理化性质，为研究其抑制剂的作用条件奠定基础．该酶作用的最适条件是30℃，pH6．0；酶在低于50℃和在pH5．15～8．75内稳定；在pH6．8，30℃下，酶催化L-DOPA氧化反应的Km和Vm分别为7．24mmol／L和617．0μmol／（L·min）．3-甲氧基-2-羟基苯甲酸、4-甲氧基-2-羟基苯甲酸、5-甲氧基-2-羟基苯甲酸、4-甲氧基-3-羟基苯甲酸和3-甲氧基-4-羟基苯甲酸等对马铃薯PPO均有明显的抑制作用，其半抑制率（IC50）分别为1．78、0．28、0．53、0．14和2．49mmol／L．抑制效应均为可逆竞争性，抑制常数分别为1．56、0．24、0．46、0．12和2．37mmol／L．

英文摘要：

Polyphenol oxidase （PPO,EC. 1.14.18.1） is an enzyme that is very important in the browning of fruit and vegetable. Browning of potato in the process of storage and process usually is caused by the effect of PPO itself. In this paper,we partly purified the PPO from potato and studied some physical and chemical characters of this enzyme. Optimum temperature and pH were determined to be 30 ℃ and 6.0,respectively. The Michaelis-Menten constant （Km） and the maximal velocity（Vm） were determined to be 7.24 mmol/L and 617.0 μmol/（L · min） at 30℃ and pH=6.8. The enzyme activity was stable at the pH ranging from 5.15-8.75 and at 50℃. The inhibitory effects of 2-hydroxy-3-methoxybenzoic acid,4-methoxysalicylic acid,5-methoxysalicylic acid,3-hydroxy-4- methoxybenzoic acid,and 4-hydroxy-3-methoxybenzoic acid on potato PPO have been studied. The inhibitor＇s concentration leading to 50 % activity lost （IC50） of them were determined to be 1.78,0. 28,0.53,0.14 and 2.49 mmol/L, respectively. The inhibition of these benzoic acid derivatives on the enzyme belongs to reversible and competitive type on the enzyme. The inhibition constant （K1） was determined to be 1.56,0.24,0.46,0.12 and 2.37 mmol/L, respectively.