Medical Research Council Mitochondrial Biology Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge CB2 0XY, United Kingdom.
J Biol Chem. 2012 Oct 5;287(41):34743-51. doi: 10.1074/jbc.M112.384560. Epub 2012 Aug 1.
In mitochondria, complex I (NADH:ubiquinone oxidoreductase) uses the redox potential energy from NADH oxidation by ubiquinone to transport protons across the inner membrane, contributing to the proton-motive force. However, in some prokaryotes, complex I may transport sodium ions instead, and three subunits in the membrane domain of complex I are closely related to subunits from the Mrp family of Na(+)/H(+) antiporters. Here, we define the relationship between complex I from Bos taurus heart mitochondria, a close model for the human enzyme, and sodium ion transport across the mitochondrial inner membrane. In accord with current consensus, we exclude the possibility of redox-coupled Na(+) transport by B. taurus complex I. Instead, we show that the "deactive" form of complex I, which is formed spontaneously when enzyme turnover is precluded by lack of substrates, is a Na(+)/H(+) antiporter. The antiporter activity is abolished upon reactivation by the addition of substrates and by the complex I inhibitor rotenone. It is specific for Na(+) over K(+), and it is not exhibited by complex I from the yeast Yarrowia lipolytica, which thus has a less extensive deactive transition. We propose that the functional connection between the redox and transporter modules of complex I is broken in the deactive state, allowing the transport module to assert its independent properties. The deactive state of complex I is formed during hypoxia, when respiratory chain turnover is slowed, and may contribute to determining the outcome of ischemia-reperfusion injury.
在线粒体中，复合物 I（NADH：泛醌氧化还原酶）利用来自 NADH 被泛醌氧化的氧化还原势能将质子穿过内膜运输，有助于质子动力势的形成。然而，在一些原核生物中，复合物 I 可能会运输钠离子，并且复合物 I 的膜结构域中的三个亚基与 Mrp 家族的 Na(+)/H(+)反向转运体的亚基密切相关。在这里，我们定义了来自牛心线粒体的复合物 I（一种人类酶的紧密模型）与线粒体内膜钠离子转运之间的关系。与当前的共识一致，我们排除了牛复合物 I 通过氧化还原偶联转运 Na(+)的可能性。相反，我们表明，当酶周转因缺乏底物而受到阻碍时，复合物 I 的“失活”形式是一种 Na(+)/H(+)反向转运体。当添加底物和复合物 I 抑制剂鱼藤酮重新激活时，该反向转运体活性被废除。它对 Na(+)具有特异性，而酵母 Yarrowia lipolytica 的复合物 I 则没有表现出这种活性，因此其失活转变的范围较小。我们提出，复合物 I 的氧化还原和转运模块之间的功能连接在失活状态下被打破，允许转运模块发挥其独立的特性。复合物 I 的失活状态是在缺氧时形成的，此时呼吸链周转减缓，可能有助于确定缺血再灌注损伤的结果。
