有机溶剂对菜青虫多酚氧化酶活力的影响

Inhibitory Effects of Some Organic Acids on the Polyphenoloxidase from the 5th Instar of Pieres rapae L.

以菜青虫五龄虫为材料,分离提取多酚氧化酶,研究有机溶剂乙醇、正丙醇、乙二醇、丙二醇、丙三醇等对该酶催化L 多巴(L DOPA)氧化活力的影响.测定抑制作用的IC50分别为12.4、6.4、24.2、15.5和17.0%.抑制剂作用的动力学研究结果表明:乙醇、乙二醇和丙三醇对酶的抑制作用表现为非竞争性类型,其抑制常数KI分别为12.05、23.50和17.53mmol/L;正丙醇和丙二醇对酶的作用表现为混合型抑制,抑制常数KI分别为4.18和12.79mmol/L,KIS分别为19.45和22.41mmol/L.

The polyphenoloxidase (PPO) is more responsible for enzymatic browning during the growth of the insects.It is also 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 synthesis---the hydroxylation of a monophenol and the oxidation of ο-diphenol to the corresponding ο-quinone.As a series of researches,in the present paper,inhibitory effects of some organic solvent on the polyphenoloxidase (PPO) from the 5^(th) instar of Pieris rapae were studied.The results showed that ethylalcohol (b),propanol (c),ethylene glycol (f),monopropylene glycol (g),glycerol (h) could inhibit the PPO activity 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 12.4、6.4、24.2、15.5和17%,respectively.The inhibitory mechanisms of compounds of b,f and h were showed to be noncompetitive type and the inhibitory constants (K_I) were determined to be 12.05、23.50 and 17.53 mmol/L,while c and g belong to be mixed typed inhibitors and their K_I are 4.18 and 12.79 mmol/L,K_(IS) are 19.45 and 22.41 mmol/L,respectively.