Bertsova Y V, Bogachev A V, Skulachev V P
Department of Bioenergetics, A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russia.
Biochim Biophys Acta. 1998 Feb 25;1363(2):125-33. doi: 10.1016/s0005-2728(97)00094-7.
Initial steps of the Azotobacter vinelandii respiratory chain have been studied on the inside-out subcellular vesicles. Two NADH:ubiquinone oxidoreductases were revealed: (i) proton-motive, capsaicin-sensitive and oxidizing dNADH as well as NADH enzyme and (ii) enzyme non-coupled to the energy conservation, capsaicin-resistant and oxidizing only NADH. The level of the oxidoreductases strongly depends upon [O2] and [NH3] in the growth medium. Increase in [O2] results in lowering of the coupled-enzyme level and in rise of the non-coupled one. Exclusion of NH3 from the growth medium increases the level of the non-coupled enzyme whereas that of the coupled enzyme remains constant. The O2-linked control of NADH:ubiquinone oxidoreductases requires CydR, a Fnr-like regulatory protein. Summarizing the above observations with those made in this group on the terminal steps of the A. vinelandii respiratory chains, one can assume that the respiratory protection of nitrogenase could be carried out by co-operation of the non-coupled NADH:ubiquinone oxidoreductase and the "partially coupled" quinoloxidase of the bd-type. Efficiency of this chain seems to be five-fold lower than that of the usual proton-motive chain (the coupled NADH:ubiquinone oxidoreductase, the Q-cycle and cytochrome oxidase of the o-type) which is also present in A. vinelandii and operates at low [O2].
已利用内翻式亚细胞囊泡对棕色固氮菌呼吸链的起始步骤进行了研究。发现了两种NADH：泛醌氧化还原酶：（i）质子动力型、对辣椒素敏感且可氧化dNADH以及NADH的酶，和（ii）与能量守恒不偶联、对辣椒素不敏感且仅氧化NADH的酶。氧化还原酶的水平在很大程度上取决于生长培养基中的[O2]和[NH3]。[O2]的增加会导致偶联酶水平降低以及非偶联酶水平升高。从生长培养基中去除NH3会增加非偶联酶的水平，而偶联酶的水平保持不变。NADH：泛醌氧化还原酶的O2相关调控需要CydR，一种Fnr样调节蛋白。将上述观察结果与该研究组对棕色固氮菌呼吸链末端步骤的观察结果进行总结，可以推测固氮酶的呼吸保护可能是通过非偶联的NADH：泛醌氧化还原酶与bd型“部分偶联”的喹啉氧化酶的协同作用来实现的。这条呼吸链的效率似乎比棕色固氮菌中也存在且在低[O2]条件下起作用的通常质子动力呼吸链（偶联的NADH：泛醌氧化还原酶、Q循环和o型细胞色素氧化酶）低五倍。
