苯甲酸及其衍生物对菜青虫多酚氧化酶抑制作用

以菜青虫五龄虫为材料,分离提取多酚氧化酶,研究苯甲酸及其衍生物:p 羟基苯甲酸、p 氰基苯甲酸、p 环已基苯甲酸等对该酶催化L 多巴(L DOPA)氧化活力的影响.测定抑制作用的IC50分别为14.2、11.3、16.1和2.1mmol/L.研究了抑制剂作用的动力学,结果表明:苯甲酸和p 环已基苯甲酸对酶的抑制作用表现为非竞争性类型,其抑制常数分别为14.25和2.21mmol/L;p 羟基苯甲酸对酶的作用表现为竞争型抑制,抑制常数KI为7.21mmol/L;p 氰基苯甲酸对酶的作用表现为混合型抑制,抑制常数KI和KIS分别为14.31和27.34mmol/L.

Inhibitory Effects of Benzoic Acid and Its Derivants on the Polyphenoloxidase from the 5th Instar of Pieres rapae L.

The polyphenoloxidase (PPO) is more responsible for enzymatic browning during the growth of the insects.It also is involved in the defense reaction and has some certain relation with the immune condition of the insects.The polyphenoloxidase is a metalloenzyme oxidase which catalyzes two distinct reactions of melanin synthesisthe hydroxylation of a monophenol and the oxidation of o-diphenol to the corresponding o-quinone.A great number of benzoic acid family compounds can inhibit the enzyme activity for the oxidation of L-DOPA.In the present paper,partial characteristics and inhibitory kinetics of polyphenoloxidase (PPO) from the 5~(th) instar of Pieris rapae L.were studied. The results show that benzoic acid,p-cyanobenzoic acid,p-hdroxybenzoic acid and p-cyclohexylbenzoic acid were chosen as inhibitors of PPO for the oxidation of L-DOPA.The reactions of these inhibitors with the PPO are reversible with remaining enzyme activity.The IC_(50) (the inhibitor concentrations leading to 50% activity lost) were estimated to be( 14.2),(16.1),11.3 and 2.1 mmol/L,respectively.The inhibitory mechanisms of p-hdroxybenzoic acid is competitive,p-cyanobenzoic acid belongs to be a mixed typed inhibitor while the others are noncompetitive inhibitors.Obviously,p-cyanobenzoic acid is the best inhibitor among the four compounds,so it may have the bright prospect in the future as the biocide.