铜铁试剂对菜青虫多酚氧化酶的抑制作用

以菜青虫Pieris rapae (L.)为试材，冰浴匀浆，4℃下6 403 ×g 离心，取上清液，经35%饱和度(NH₄)₂SO₄沉淀，Sephadex G100凝胶过滤柱层析等分离步骤，获得部分纯化的菜青虫多酚氧化酶制剂。研究不同浓度铜离子及铜铁试剂对该酶的影响，结果表明：Cu₂₊在0～0.100 mmol/L范围内对酶活力表现激活作用；浓度大于0.125 mmol/L时表现抑制作用，其IC₅₀为0.651±0.022 mmol/L；铜铁试剂对该酶抑制作用的IC₅₀为0.100±0.012 mmol/L。抑制动力学研究结果表明：铜铁试剂对该酶表现为可逆抑制效应，为竞争性抑制类型，其抑制常数K_i为0.076±0.013 mmol/L。

Inhibitory effect of cupferron on the activity of polyphenoloxidase from Pieris rapae (L.) (Lepidoptera: Pieridae)

The kinetic properties of polyphenoloxidase (PPO) from Pieris rapae (L.) were studied after the enzyme was partially purified by 35% saturated (NH₄)₂SO₄ and chromatographed on a Sephadex G-100 gel filtration. Meanwhile, the effects of PPO on the oxidation of L-DOPA by adding copper ion or cupferron were also studied. The results showed that the activity of PPO was enhanced by Cu₂₊ in the concentration of 0-0.100 mmol/L; however, the activity was inhibited by the same ion when the concentration was over 0.125 mmol/L, and the IC₅₀ was estimated to be 0.651±0.022 mmol/L. The results also indicated that the reaction of cupferron with the PPO is a reversible course with remaining enzyme activity, the inhibitory mechanism belongs to be the competitive type and the IC₅₀ was estimated to be 0.100±0.012 mmol/L. Furthermore, the equilibrium constant for cupferron was determined to be 0.076±0.013 mmol/L. 