几种苯甲酸族化合物对菜青虫多酚氧化酶的抑制作用

Inhibitory Effects of Some Benzoic Acid Family Compounds on the Polyphenoloxidase from the 5^(th) Instar of Pieres rapae L.

以菜青虫五龄幼虫为材料,分离提取多酚氧化酶,研究对醛基苯甲酸(a)、对甲氧基苯甲酸(b)、对异丙基苯甲酸(c)、对环已基苯甲酸(d)、对氟苯甲酸(e)、对氯苯甲酸(f)和对溴苯甲酸(g)等苯甲酸族化合物,对该酶催化L-多巴(L-DOPA)氧化活力的影响.测定(a),(b),(c),(d)和(f)抑制作用的IC50分别为10.63、12.22、1.75、2.10和6.64 mmol/L,而(e)和(g)则没有明显的抑制效果.研究上述效应物的抑制作用动力学,结果表明:(a)、(c)和(f)对酶的作用表现为竞争性抑制,其抑制常数分别为6.74、1.08和3.94 mmol/L;(b)和(d)对酶的抑制作用表现为非竞争性类型,其抑制常数分别为13.11和2.21 mmol/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 hyroxylation of a monophenol and the oxidation of o-diphenol to the corresponding o-quinone. In the present paper, the effects of some benzoic acid family compounds on the polyphenoloxidase from the 5^th instar of Pieres rapae L. were studied. The results show that terephthalaldhyic acid,p-anisic acid,p-isopropylbenzoic acid, p-cyclohexylbenzoic acid and p-chlorobenzoic acid have potent inhibition on the enzyme for the oxidation of L- DOPA. The ICs0 ,the inhibitor concentrations leading to 50% activity lost, were estimated to be 10.63,12.22,1.75,2.10 and 6.64 mmol/L,respectively. The inhibitory kinetics was studied and the results showed that terephthalaldhydic acid, p-isopropylbenzoic acid and p-chlorobenzoic acid were competitive inhibitors,while p-anisic acid and p-cyclohexylbensoic acid were noncompetitive inhibitors. Their inhibition constants were determined and compared. Obviously, the inhibitory effects of p-isopropylbenzoie acid and p- cyclohexylbenzoic acid were higher than the other compounds, so they may have the bright prospect in the future as the biocide.