Molenaar D, van der Rest M E, Petrović S
Biotechnologisches Zentrallabor, Heinrich-Heine-Universität, Düsseldorf, Germany.
Eur J Biochem. 1998 Jun 1;254(2):395-403. doi: 10.1046/j.1432-1327.1998.2540395.x.
In addition to a cytoplasmic, NAD-dependent malate dehydrogenase (EC 1.1.1.37), Corynebacterium glutamicum possesses a highly active membrane-associated malate dehydrogenase (acceptor) (EC 1.1.99.16). This enzyme also takes part in the citric acid cycle. It oxidizes L-malate to oxaloacetate and donates electrons to ubiquinone-1 and other artificial acceptors or, via the electron transfer chain, to oxygen. NAD is not an acceptor and the natural direct acceptor for the enzyme is most likely a quinone. The enzyme is therefore called malate:quinone oxidoreductase, abbreviated to Mqo. Mqo is a peripheral membrane protein and can be released from the membrane by addition of chelators. The solubilized form was partially purified and characterized biochemically. FAD is probably a tightly but non-covalently bound prosthetic group, and the enzyme is activated by lipids. A C. glutamicum mutant completely lacking Mqo activity was isolated. It grows poorly on several substrates tested. The mutant possesses normal levels of cytoplasmic NAD-dependent malate dehydrogenase. A plasmid containing the gene from C. glutamicum coding for Mqo was isolated by complementation of the Mqo-negative phenotype. It leads to overexpression of Mqo activity in the mutant. The nucleotide sequence of the mqo gene was determined and is the first sequence known for this enzyme. The derived protein sequence is similar to hypothetical proteins from Escherichia coli, Klebsiella pneumoniae, and Mycobacterium tuberculosis.
除了一种胞质内依赖NAD的苹果酸脱氢酶（EC 1.1.1.37）外，谷氨酸棒杆菌还拥有一种活性很高的膜结合苹果酸脱氢酶（受体）（EC 1.1.99.16）。这种酶也参与柠檬酸循环。它将L-苹果酸氧化为草酰乙酸，并将电子传递给泛醌-1和其他人工受体，或者通过电子传递链传递给氧气。NAD不是该酶的受体，其天然直接受体很可能是一种醌。因此，该酶被称为苹果酸：醌氧化还原酶，简称为Mqo。Mqo是一种外周膜蛋白，通过添加螯合剂可将其从膜上释放下来。对溶解后的形式进行了部分纯化并进行了生化特性分析。FAD可能是一种紧密但非共价结合的辅基，该酶被脂质激活。分离出了一个完全缺乏Mqo活性的谷氨酸棒杆菌突变体。它在几种测试底物上生长不良。该突变体的胞质内依赖NAD的苹果酸脱氢酶水平正常。通过对Mqo阴性表型的互补作用，分离出了一个含有谷氨酸棒杆菌编码Mqo基因的质粒。它导致突变体中Mqo活性的过表达。测定了mqo基因的核苷酸序列，这是该酶已知的第一个序列。推导得到的蛋白质序列与大肠杆菌、肺炎克雷伯菌和结核分枝杆菌的假定蛋白质相似。
