The respiratory substrate rhodoquinol induces Q-cycle bypass reactions in the yeast cytochrome bc1 complex -: Mechanistic and physiological implications
The respiratory substrate rhodoquinol induces Q-cycle bypass reactions in the yeast cytochrome bc1 complex -: Mechanistic and physiological implications
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DOI：
10.1074/jbc.m507616200
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发表时间：
2005-10-14
影响因子：
4.8
通讯作者：
Kramer, DM
中科院分区：
文献类型：
--
作者：
Cape, JL;Strahan, JR;Kramer, DM
线粒体细胞色素bc（1）复合物催化电子从泛醇转移到细胞色素c，同时通过“Q循环”机制产生ATP合成的质子动力。在某些条件下，通过Q-循环的电子流在酶的醌醇氧化酶位点的反应性中间体水平上被阻断，导致“旁路反应”，其中一些导致超氧化物的产生。使用类似物的呼吸底物泛醇-3和rhodoquinol-3，我们表明，Q-循环旁路反应的相对速率在酿酒酵母细胞Bc 1复合物是高度依赖于由高达100倍的因子上的底物醌醇的属性。我们的研究结果表明，Q-循环旁路反应的速率取决于在酶的醌醇氧化酶位点产生的活性中间体的稳态浓度。我们的结论是，正常运行的Q-循环需要一个相当窄的窗口的氧化还原电位相对于对苯二酚基板，以允许正常营业额的复杂，同时防止潜在的破坏性旁路反应。
The mitochondrial cytochrome bc(1) complex catalyzes the transfer of electrons from ubiquinol to cyt c while generating a proton motive force for ATP synthesis via the "Q-cycle" mechanism. Under certain conditions electron flow through the Q-cycle is blocked at the level of a reactive intermediate in the quinol oxidase site of the enzyme, resulting in "bypass reactions," some of which lead to superoxide production. Using analogs of the respiratory substrates ubiquinol-3 and rhodoquinol-3, we show that the relative rates of Q-cycle bypass reactions in the Saccharomyces cerevisiae cyt bc1 complex are highly dependent by a factor of up to 100-fold on the properties of the substrate quinol. Our results suggest that the rate of Q-cycle bypass reactions is dependent on the steady state concentration of reactive intermediates produced at the quinol oxidase site of the enzyme. We conclude that normal operation of the Q-cycle requires a fairly narrow window of redox potentials with respect to the quinol substrate to allow normal turnover of the complex while preventing potentially damaging bypass reactions.