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中文摘要：
采用分光光度法和凝胶过滤色谱法研究了L-半胱氨酸抑制多酚氧化酶（PPO）活性的机理。结果表明：以邻苯二酚为底物时,PPO酶促反应产物与L-半胱氨酸结合生成的无色硫氢化合物在295nm处有最大吸收,可作为测定PPO活性的检测波长;分别在410nm和295nm波长下检测醌类物质和硫氢化合物时,已生成的醌类物质可迅速与L-半胱氨酸结合,使410nm处的吸光度迅速降低,而295nm处的则迅速升高;经50mmol/LL-半胱氨酸处理30min的PPO酶液经凝胶过滤色谱分离之后其活性基本没有变化。研究认为：L-半胱氨酸并不是通过对PPO活性中心的结构性修饰,或是发生共价结合来抑制其活性,而是直接与其酶促反应产物——醌类物质结合生成无色的硫氢化合物,从而抑制褐变的发生。利用这一抑制原理,可改进PPO酶活的测定方法。
英文摘要：
The inhibition mechanism of L-cysteine on polyphenoloxidase （PPO） was studied by spectrophotometry and gel filtration chromatography. The results from PPO oxidized product analysis by spectrophotometer implied that the sulfhydryl compound has the maximal absorbance at 295 nm with catechol as the substrate, which may be used as the assay wavelength. As quinone reacts with L-cysteine, the absorbance at 295 nm increases rapidly, while the absorbance at 410 nm decreases, When the PPO was treated with 50 mmol/L L-cysteine for 30 min, the enzyme activity did not decrease at all, after being isolated by gel filtration chromatography. The results indicated that L-cysteine inhibites the browning reaction due to the formation of a colourless compound, but does not involve a direct inhibition on PPO active site or form a covalently-bounded complex between PPO and L-cysteine. The PPO measurement method can be modified in terms of this inhibition mechanism.
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