Abstract：
Malate dehydrogenase (EC 1.1.1.37) was purified to homogeneity from the phototrophic purple non-sulfur bacterium Rhodovulum steppense A-20s. According to gel-chromatography and electrophoretic studies, malate dehydrogenase is present as a dimer, tetramer and octamer depending on cultivation conditions. In phototrophic aerobic conditions only the tetrameric form was present, in chemotrophic aerobic conditions all three forms were detected, while in the absence of oxygen the octameric form disappeared. The malate dehydrogenase oligomers are encoded by a single gene and composed of the same 35 kDa polypeptide but differ in pH and temperature optimum, in affinities to malate, oxaloacetate, NADH and NAD+ and in regulation by cations and citrate. By modulating the cultivation conditions, it has been established that the dimer participates in the glyoxylate cycle; the tetramer operates in the tricarboxylic acid cycle, and the octamer may be involved in the adaptation to oxidative stress.
摘要：
苹果酸脱氢酶（EC1.1.1.37）从光养紫色非硫细菌RhodovulumsteppaseA-20s中纯化至同质。根据凝胶色谱和电泳研究，苹果酸脱氢酶以二聚体形式存在，四聚体和八聚体取决于培养条件。在光养好氧条件下，仅存在四聚体形式，在化学营养有氧条件下，所有三种形式都被检测到，而在没有氧气的情况下，八聚体形式消失了。苹果酸脱氢酶寡聚体由单个基因编码，由相同的35kDa多肽组成，但在最适pH和温度方面不同，与苹果酸的亲和力，草酰乙酸,NADH和NAD+并受阳离子和柠檬酸盐的调节。通过调节栽培条件,已经确定二聚体参与乙醛酸循环;四聚体在三羧酸循环中运行，八聚体可能参与对氧化应激的适应。
