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首页> 外文期刊>The FEBS journal >Reduction of ferredoxin or oxygen by flavin-based electron bifurcation in Megasphaeraelsdenii
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Reduction of ferredoxin or oxygen by flavin-based electron bifurcation in Megasphaeraelsdenii

机译：黄Mega中基于黄素的电子分叉还原铁氧还蛋白或氧

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Over 50years ago, it was reported that, in the anaerobic rumen bacterium Megasphaeraelsdenii, the reduction of crotonyl-CoA to butyryl-CoA by NADH involved an electron transferring flavoprotein (Etf) as mediator [Baldwin RL, Milligan LP (1964) Biochim Biophys Acta 92, 421-432]. Purification and spectroscopic characterization revealed that this Etf contained 2 FAD, whereas, in the Etfs from aerobic and facultative bacteria, one FAD is replaced by AMP. Recently we detected a similar system in the related anaerobe Acidaminococcusfermentans that differed in the requirement of additional ferredoxin as electron acceptor. The whole process was established as flavin-based electron bifurcation in which the exergonic reduction of crotonyl-CoA by NADH mediated by Etf+butyryl-CoA dehydrogenase (Bcd) was coupled to the endergonic reduction of ferredoxin also by NADH. In the present study, we demonstrate that, under anaerobic conditions, Etf+Bcd from M.elsdenii bifurcate as efficiently as Etf+Bcd from A.fermentans. Under the aerobic conditions used in the study by Baldwin and Milligan and in the presence of catalytic amounts of crotonyl-CoA or butyryl-CoA, however, Etf+Bcd act as NADH oxidase producing superoxide and H2O2, whereas ferredoxin is not required. We hypothesize that, during bifurcation, oxygen replaces ferredoxin to yield superoxide. In addition, the formed butyryl-CoA is re-oxidized by a second oxygen molecule to crotonyl-CoA, resulting in a stoichiometry of 2 NADH consumed and 2H(2)O(2) formed. As a result of the production of reactive oxygen species, electron bifurcation can be regarded as an Achilles' heel of anaerobes when exposed to air.
机译：超过50年前，据报道，在厌氧瘤胃细菌Megasphaeraelsdenii中，NADH将巴豆酰-CoA还原为丁酰-CoA涉及一种电子转移黄素蛋白（Etf）作为介体[Baldwin RL，Milligan LP（1964）Biochim Biophys Acta 92，421-432]。纯化和光谱表征表明该Etf包含2个FAD，而在好氧和兼性细菌的Etfs中，一个FAD被AMP取代。最近，我们在相关的厌氧菌酸氨基球菌发酵菌中检测到了类似的系统，该系统在添加铁氧还蛋白作为电子受体的要求上有所不同。整个过程被建立为基于黄素的电子分叉，其中Etf +丁酰-CoA脱氢酶（Bcd）介导的NADH对巴豆酰-CoA的强能还原与NADH对铁氧还蛋白的雌激素还原相结合。在当前的研究中，我们证明，在厌氧条件下，来自埃尔氏假单胞菌的Etf + Bcd与发酵曲霉的Etf + Bcd一样有效。然而，在鲍德温和米利根在研究中使用的有氧条件下，在催化量的巴豆酰-CoA或丁酰-CoA的存在下，Etf + Bcd可以作为NADH氧化酶，产生超氧化物和H2O2，而不需要铁氧还蛋白。我们假设在分叉过程中，氧气取代了铁氧还蛋白，从而产生超氧化物。此外，形成的丁酰辅酶A被第二个氧分子再氧化为巴豆酰辅酶A，导致化学计量为2 NADH消耗，形成2H（2）O（2）。由于产生了活性氧，当暴露在空气中时，电子分叉可被视为厌氧菌的致命弱点。

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