Characterization of ubisemiquinone radical in the cytochrome b-c1 segment of the mitochondrial respiratory chain.
Characterization of ubisemiquinone radical in the cytochrome b-c1 segment of the mitochondrial respiratory chain.
复制标题
线粒体呼吸链细胞色素 b-c1 片段中泛半醌自由基的表征。
DOI：
10.1016/0003-9861(81)90517-8
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发表时间：
1981
影响因子：
3.9
通讯作者：
King,TE
中科院分区：
文献类型：
--
作者：
Nagaoka,S;Yu,L;King,TE
在还原型泛醌-细胞色素c还原酶（B− c 1-III复合物）中的泛醌蛋白质QP-C在催化量的琥珀酸脱氢酶和QP-S存在下被琥珀酸还原时显示出稳定的泛半醌自由基。在室温下，使用EPR技术，在氧化还原染料或琥珀酸酯/富马酸酯对存在下，B− c 1-III络合物的氧化还原滴定显示，泛半醌自由基在pH 8.0下具有约+ 67 mV的中点电位。进一步分析得到E1为+ 83 mV，E2为+ 51 mV，分别对应于（QH 2 QH·）和（QH· Q）或其他电子化形式。平衡自由基浓度已被发现受pH值和琥珀酸/富马酸对。在pH 9.0时，自由基的振幅和稳定性最大。pH低于7.0时，几乎没有检测到自由基。用微波功率饱和法研究了泛半醌自由基的电子自旋弛豫行为，结果表明QP-C的泛半醌自由基与其它顺磁中心有一定的隔离。本文详细研究了磷脂、QP-S和其它试剂对泛醌自由基形成以及QP-C酶活性的影响。
The ubiquinone protein, QP-C, in reduced ubiquinone-cytochrome c reductase (the b− c 1-III complex) shows a stable ubisemiquinone radical when the enzyme is reduced by succinate in the presence of catalytic amounts of succinate dehydrogenase and QP-S. At room temperature using EPR technique the redox titration of the b− c 1-III complex in the presence of redox dyes or succinate/fumarate couple reveals that the ubisemiquinone radical has a midpoint potential of approximately+ 67 mV at pH 8.0. Further analysis yields E 1 of+ 83 mV and E 2 of+ 51 mV corresponding to (QH 2 QH·) and (QH· Q) or other electronated forms, respectively. The equilibrium radical concentration has been found to be affected both by pH and succinate/fumarate couple. At pH 9.0 the radical shows the maximal amplitude and stability. Below pH 7.0, little radical was detected. The electron spin relaxation behavior of ubisemiquinone radical, as examined by microwave power saturation, indicates that the ubisemiquinone radical of QP-C is somewhat isolated from other paramagnetic centers. The effects of phospholipids, QP-S, and other agents on ubisemiquinone radical formation as well as the enzymatic activity of QP-C have been studied in detail.