Properties of a semiquinone anion located in the QH2:Cytochrome c oxidoreductase segment of the mitochondrial respiratory chain
Properties of a semiquinone anion located in the QH2:Cytochrome c oxidoreductase segment of the mitochondrial respiratory chain
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位于 QH2 的半醌阴离子的特性：线粒体呼吸链的细胞色素 c 氧化还原酶片段
DOI：
10.1016/0014-5793(80)80422-4
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发表时间：
1980
期刊：
影响因子：
3.5
通讯作者：
E. C. Slater
中科院分区：
文献类型：
--
作者：
S. Vries;J. Berden;E. C. Slater
电子从泛醇转移到细胞色素c的方式仍在讨论中。电位滴定和光学监测的前稳态动力学测量的结果，主要给出了细胞色素的氧化还原性质的信息，导致了通过QH的电子转移的建议[1，2]：细胞色素c氧化还原酶，其中半醌的形成是电子转移的先决条件。在呼吸链制剂中存在的半醌确实已通过EPR研究确定[3-IO]。Ohnishi和Trumpower在分离的琥珀酸酯中检测到两种不同的泛半醌群：细胞色素c氧化还原酶[101，SQ，和SQ，弛豫时间不同（另见11 r11）。本文的结果表明，在QH中存在一种非常稳定的半醌阴离子：细胞色素c氧化还原酶，可能对应于[lo]中的SQ。半醌阴离子的EPR信号的定量表明，最大浓度是细胞色素Cr的1/2。为了充分描述pH值对能斯特方程中半醌阴离子浓度的影响，必须考虑半醌阴离子结合位点的有限容量。
The way in which electrons are transferred from ubiquinol to cytochrome c is still under discussion. The results of potentiometric titrations and measurements of the pre-steady-state kinetics monitored optically, mainly giving information on the redox properties of the cytochromes, have led to proposals [1, 2] for electron transfer through QH,: cytochrome c oxidoreductase, in which the formation of a semiquinone is a prerequisite for electron transfer. The presence of a semiquinone in preparations of the respiratory chain has, indeed, been identified by EPR studies [3-IO]. Ohnishi and Trumpower have detected two different populations of ubisemiquinone in isolated succinate: cytochrome c oxidoreductase [101, SQ, and SQ,, differing in relaxation time (see also11 r11.The results in this paper indicate the existence of a very stable semiquinone anion located in QH,: cytochrome c oxidoreductase, presumably corresponding to SQ, in [lo]. Quantitation of the EPR signal of the semiquinone anion showed that the maximal concentration is I/2 that of the cytochrome cr. In order adequately to describe the effect of pH on the semiquinone anion concentration in the Nernst equation, a Limited capacity of the binding site for the semiquinone anion must be taken into account.