Abstract

One isoform of NADP⁺-dependent decarboxylating malate dehydrogenase (EC 1.1.1.40) was found in the leaf mesophyll of corn. The enzyme was purified in four stages: homogenization, fractionation with ammonium sulfate, gel filtration on Sephadex G-25, and ion exchange on Sephacel. The specific activity of the purified, electrophoretically homogeneous preparation was 92 E/mg of protein, while its yield was 15%, and the purification degree was 109. The relative electrophoretic mobility of the decarboxylating malate dehydrogenase was 0.1. The optimal pH for enzyme functioning during the catalysis of forward and reverse reactions was 8.0. The Michaelis constants were determined for the direct and reverse reactions: 5.5 mM for malate and 1.3 mM for pyruvate. Moreover, the affinity for coenzymes varied significantly. Thus, K_M was equal to 4.5 mM for NADP⁺ and 0.9 mM for NADP.

中文翻译：

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玉米叶片NADP +依赖性脱羧苹果酸脱氢酶的动力学性质

摘要

NADP的一种亚型⁺玉米叶片的叶肉中发现了依赖的脱羧苹果酸脱氢酶（EC 1.1.1.40）。酶的纯化分为四个阶段：匀浆，用硫酸铵分级分离，在Sephadex G-25上进行凝胶过滤以及在Sephacel上进行离子交换。纯化的电泳均质制剂的比活为92 E / mg蛋白，产率为15％，纯化度为109。苹果酸脱羧化苹果酸脱氢酶的相对电泳迁移率为0.1。在正向和反向反应的催化过程中，酶功能的最佳pH为8.0。确定了直接反应和反向反应的米氏常数：苹果酸为5.5 mM，丙酮酸为1.3 mM。此外，对辅酶的亲和力差异很大。因此，K _M对于NADP ⁺等于4.5 mM，对于NADP等于0.9 mM。