热动力学研究L-抗坏血酸和Cu^(2+)对过氧化氢酶的协同抑制

Thermokinetic Studies on the Cooperative Inhibition of Catalase by L-Ascorbic Acid and Cu^(2+)

在 310 15K ,pH =7 0的 0 1mol·L-1Na2 HPO4 NaH2 PO4 缓冲溶液中 ,利用热动力学方法研究了L 抗坏血酸 ,Cu2 +及二者同时存在时 ,过氧化氢酶催化H2 O2 分解反应的动力学规律 .发现L 抗坏血酸和Cu2 +单独存在时对酶反应没有明显的抑制作用 ,二者共存时 ,对反应有非线性抑制作用 .在一定的酶和底物浓度下 ,L 抗坏血酸和Cu2 +不影响总反应的一级速率方程的形式 ,只减小了一级反应速率常数 .酶活性随抑制剂浓度变化关系呈S形曲线 .结合实验结果和文献 ,提出了一种L 抗坏血酸和Cu2

The reaction of catalase catalyzed decomposition of H2O2 was studied by thermokinetic method in 0.1 mol.L-1 Na2HPO4-NaH2PO4 buffer solution at 310.15 K and pH 7.0 in the presence of L-ascorbic acid or Cu2+ or of the both. There is no apparent inhibition effect on catalase when L-ascorbic acid or Cu2+ is present solely. However, when they are present simultaneously, a non-linear inhibition of the reaction can be observed. At definite enzyme and substrate concentrations, L-ascorbic acid and Cu2+ have no effect on the form of kinetic equation of the overall reaction. In other words, the overall reaction of H2O2 decomposition catalyzed by catalase is according to pseudo-first order rate equation when L-ascorbic and Cu2+ are present or absent, but the rate constant decrease when the concentrations of L-ascorbic and Cu2+ increase. Dose relation of the enzyme activity with the concentrations of L-ascorbic and Cu2+ is a sigmoidal curve. Combined the results of this experiment with the conclusions of literatures, a possible mechanism of L-ascorbic acid and Cu2+ cooperative inhibition on catalase was proposed.