Kinetic evidence against partitioning of the ubiquinone pool and the catalytic relevance of respiratory-chain supercomplexes
Kinetic evidence against partitioning of the ubiquinone pool and the catalytic relevance of respiratory-chain supercomplexes
复制标题
DOI：
10.1073/pnas.1413855111
复制
发表时间：
2014-11-04
影响因子：
11.1
通讯作者：
Hirst, Judy
中科院分区：
文献类型：
--
作者：
Blaza, James N.;Serreli, Riccardo;Hirst, Judy
在线粒体中，四种呼吸链复合物通过维持穿过内膜的质子动力来驱动氧化磷酸化，该质子动力用于合成 ATP。随着呼吸链超级复合物的表征，内膜密集的蛋白质如何组织以优化结构和功能的问题再次受到重视。超复合物是越来越被接受的结构实体，但其功能和催化优势存在争议。值得注意的是，相对于可自由接近的共同底物库提供的速率，超复合物中酶之间的底物“通道”被认为具有动力学优势。在这里，我们重点关注线粒体泛醌/泛醇库。我们制定并测试了哺乳动物呼吸链行为的三个概念上简单的预测，这些预测取决于超复合物中的通道在动力学上是否重要，以及泛醌库是否在路径之间分配。我们的光谱和动力学实验证明了 NADH 和琥珀酸氧化的代谢途径如何通过单一的、普遍可用的未分区或通道的泛醌/泛醇池进行通信和催化。我们重新评估了来自通量控制分析的主要相反证据，发现底物通道的结论来自于单一抑制剂的特定行为；我们解释了为什么不同的抑制剂表现不同，并表明强大的通量控制分析没有提供沟道的证据。最后，我们讨论了呼吸链超级复合物的形成如何为能量转换膜带来其他优势。
In mitochondria, four respiratory-chain complexes drive oxidative phosphorylation by sustaining a proton-motive force across the inner membrane that is used to synthesize ATP. The question of how the densely packed proteins of the inner membrane are organized to optimize structure and function has returned to prominence with the characterization of respiratory-chain supercomplexes. Supercomplexes are increasingly accepted structural entities, but their functional and catalytic advantages are disputed. Notably, substrate "channeling" between the enzymes in supercomplexes has been proposed to confer a kinetic advantage, relative to the rate provided by a freely accessible, common substrate pool. Here, we focus on the mitochondrial ubiquinone/ubiquinol pool. We formulate and test three conceptually simple predictions of the behavior of the mammalian respiratory chain that depend on whether channeling in supercomplexes is kinetically important, and on whether the ubiquinone pool is partitioned between pathways. Our spectroscopic and kinetic experiments demonstrate how the metabolic pathways for NADH and succinate oxidation communicate and catalyze via a single, universally accessible ubiquinone/ubiquinol pool that is not partitioned or channeled. We reevaluate the major piece of contrary evidence from flux control analysis and find that the conclusion of substrate channeling arises from the particular behavior of a single inhibitor; we explain why different inhibitors behave differently and show that a robust flux control analysis provides no evidence for channeling. Finally, we discuss how the formation of respiratory-chain supercomplexes may confer alternative advantages on energy-converting membranes.