金属离子对菜青虫酚氧化酶活力的影响

Effects of Some Metal Ions on the Activity of Phenoloxidase from Pieris rapae L.

以菜青虫五龄幼虫为材料,冰浴匀浆,在4℃下8000r/min离心,取上清液,经35%饱和(NH4)2SO4沉淀,经SephadexG100凝胶柱层析等步骤分离,获得部分纯化的菜青虫酚氧化酶制剂.研究多种金属离子对该酶活性的影响,结果表明:碱金属离子K+、Li+和Na+对酶活力没有影响.碱土金属离子Mg2+、Ba2+和Ca2+对酶有激活作用,激活作用的大小顺序为Mg2+>Ca2+>Ba2+.过渡金属离子Mn2+、Co2+、Cu2+和Zn2+对酶活力的影响呈现不同的效应,Mn2+、Co2+和Zn2+对该酶活性有不同程度的激活作用,Cu2+浓度在0.10mmol/L内对该酶有一定的激活作用,浓度大于0.13mmol/L为抑制作用,其IC50为0.65mmol/L.重金属离子Hg2+、Cd2+和Pb2+对酶活力有不同程度的激活作用,以Hg2+的激活作用最为显著.

Phenoloxidase is 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.Phenoloxidase is a metalloenzyme oxidase which catalyzes two distinct reactions of melanin synthesis:the hydroxylation of monophenol and the oxidation of ο-diphenol to the corresponding ο-quinone.As a series of researches,in the present paper,effects of some metal ions on the activity of phenoloxidase from the 5~th instar of Pieris rapae L.were studied.The results showed that K+,Li+ and Na+ had no any effects on the activity of the tested enzyme.Mg^2+ ,Ba^2+ and Ca^2+ activated the enzyme and the activated order following:Mg^2+ >Ca^2+ >Ba^2+ .The transitional metal ions had different effects on the activity of the enzyme.Mn^2+ 、Co^2+ and Zn^2+ activated the enzyme.Cu^2+ had different behaviors.At low concentration (lower than 0.10 mmol/L) Cu^2+ could enhance the enzyme activity,but,at high concentration (higher than 0.13 mmol/L) Cu^2+ could inhibit the enzyme and its IC_50 was estimated to be 0.65 mmol/L.The results also indicated that Hg^2+ ,Cd^2+ and Pb^2+ enhanced the enzyme activity and Hg^2+ was a more efficacious activator in the heavy metal ions what we had determined.