Abstract: The enzyme active center essential groups of polyphenol oxidase（PPO）from potato and its inhibitory mechanism were investigated. The essential groups of PPO active center are determined that imidazole of His，guanidinium of Arg and Trp residue，disulfide bond have contribution to the stability of active centre structure but dissociative sulfhydryl group is not the essential group for PPO react activity. These are concluded by the result of using chemical modifiers such as BrAC，Hacac，NBS，DTT and pCMB react with PPO since they have relative specificity to correspond amino acid active group. Inhibit kinetics experiments show that the 50% enzyme activity inhibit concentration（IC₅₀）of ethanol and benzoic acid are 0.12 mmol/L and 0.07 mmol/L respectively，the inhibitory mechanism of ethanol and benzoic acid to PPO are competitive and noncompetitive reversible inhibition. These results show that ethanol inhibits PPO activity by combining with enzyme active center，while benzoic acid inhibits PPO activity by combining with non-enzyme active center.

Key words: polyphenol oxidase, enzyme active center, essential group, reversible inhibition, potato

摘要： 探讨源于马铃薯多酚氧化酶（PPO）的酶活性中心必需基团组成与抑制剂对PPO的抑制作用类型。应用具有相对专一性的氨基酸基团化学修饰剂溴乙酸（BrAC）、乙酰丙酮（Hacac）、N-溴代琥珀酰亚胺（NBS）、1,4-二硫代苏糖醇（DTT）与对氯汞苯甲酸（pCMB）等对PPO进行化学修饰反应，确定源于马铃薯的多酚氧化酶活性中心必需基团组成为组氨酸（His）的咪唑基、精氨酸（Arg）的胍基与色氨酸（Trp）残基，二硫键对酶活性中心的稳定有贡献作用但游离的硫基不是酶反应所必需的基团。抑制动力学实验表明乙醇对PPO的半抑制浓度（IC₅₀）为0.12 mmol/L，抑制类型为竞争性可逆抑制，苯甲酸对PPO的IC₅₀为0.07 mmol/L，抑制类型为非竞争性可逆抑制。说明乙醇通过与PPO酶活中心结合抑制PPO酶活性而苯甲酸则通过与PPO非酶活中心的结合抑制PPO酶活。

关键词: 多酚氧化酶, 酶活性中心, 必需基团, 可逆抑制, 马铃薯