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首页> 外文期刊>Biochemistry >A Mutation in Na+-NQR Uncouples Electron Flow from Na+ Trans location in the Presence of K+
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A Mutation in Na+-NQR Uncouples Electron Flow from Na+ Trans location in the Presence of K+

机译：Na + -NQR的突变使存在K +的Na +反式电子流解耦

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摘要

The sodium-pumping NADH:ubiquinone oxidoreductase (Na+-NQR) is a bacterial respiratory enzyme that obtains energy from the redox reaction between NADH and ubiquinone and uses this energy to create an electrochemical Na(+)gradient across the cell membrane. A number of acidic residues in transmembrane helices have been shown to be important for Na+ translocation. One of these, Asp-397 in the NqrB subunit, is a key residue for Na+ uptake and binding. In this study, we show that when this residue is replaced with asparagine, the enzyme acquires a new sensitivity to K+; in the mutant, K+ both activates the redox reaction and uncouples it from the ion translocation reaction. In the wild-type enzyme, Na+ (or Li+) accelerates turnover while K+ alone does not activate. In the NqrB-D397N mutant, K+ accelerates the same internal electron transfer step (2Fe-2S -> FMNC) that is accelerated by Na+. This is the same step that is inhibited in mutants in which Na+ uptake is blocked. NqrB-D397N is able to translocate Na+ and Li+, but when K+ is introduced, no ion translocation is observed, regardless of whether Na+ or Li+ is present. Thus, this mutant, when it turns over in the presence of K+, is the first, and currently the only, example of an uncoupled Na+-NQR. The fact the redox reaction and ion pumping become decoupled from each other only in the presence of K+ provides a switch that promises to be a useful experimental tool.
机译：钠泵吸NADH：泛醌氧化还原酶（Na + -NQR）是一种细菌呼吸酶，可从NADH和泛醌之间的氧化还原反应中获得能量，并利用该能量在细胞膜上产生电化学Na（+）梯度。跨膜螺旋中的许多酸性残基已显示对Na +易位很重要。其中之一，NqrB亚基中的Asp-397，是Na +吸收和结合的关键残基。在这项研究中，我们表明当该残基被天冬酰胺取代时，该酶对K +具有新的敏感性。在突变体中，K +既激活氧化还原反应，又将其与离子转运反应解偶联。在野生型酶中，Na +（或Li +）可加速周转，而单独的K +则不能激活。在NqrB-D397N突变体中，K +加速了与Na +加速相同的内部电子转移步骤（2Fe-2S-> FMNC）。这与阻止Na +吸收的突变体所抑制的步骤相同。 NqrB-D397N能够转运Na +和Li +，但是当引入K +时，无论是否存在Na +或Li +，都没有观察到离子易位。因此，该突变体在存在K +的情况下翻转时，是第一个（也是目前唯一的）未偶联的Na + -NQR实例。仅在存在K +的情况下，氧化还原反应和离子泵浦才相互分离，这一事实提供了一个有望成为有用的实验工具的开关。

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