中华猕猴桃蛋白酶热失活动力学

改进了酶的提纯方法获得聚焦电泳为单一区带酶制剂。酶热失活以 HbCO 为底物时为一级反应,动力学方法表明 HbCO 对酶的热失活有保护作用,68.90℃时k_(+0)/k′_(+3)比值24,“HbCO”络合物活化能 535kJ/mol,焓 531 kJ/mol,自由能 116kJ/mol,熵1 212kJ/mol,生成自由能和生成热分别为20和209kJ/mol,这些参数说明 HbCO对酶热失活保护作用以及对酶构象影响可能与二者的多键结合和HbCO 水化作用有关。本文中还得到CBZ-Lys-ONp 为底物的热力学参数,观察到 DTT 对酶热失活保护是很小的。

Kinetics of the Thermal Inactivation of Actinidin

Actinidin which was homogeneous in SDS and isoelectrofocusing was obtained by an improved method. Kinetic analysis of the thermal inactivation of the enzyme showed a first order or second order reaction when HbCO or CBZ-Lys-ONp was used as substrate respectively. The thermal parameters of both reactions were calculated. From the effect of temperature on the rate constants and on the complex formation had been calculated. The formation of the complex involved a AH of 205 kJ/ mol and a AS of 132 e. u/ mol, whereas the activation entropy of the co mplex was 290 e. u/ mol as compared with a value of 4 e. u/ mol for the free enzyme. It appears that the binding of HbCO led to some significant comformational changes which in turn were responsible for both the activating and stabilizing effect against thermal inactivation. But the effect by DTT was found to be obscure.