关键词: 菜青虫, 多酚氧化酶, 铜离子, 铜铁试剂, 抑制作用

Abstract: 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. 

Key words: Pieris rapae, polyphenoloxidase, copper ion, cupferron, inhibition