Zhu Q S, Beattie D S
Department of Biochemistry, West Virginia University, School of Medicine, Morgantown 26506.
J Biol Chem. 1988 Jan 5;263(1):193-9.
The reduction of the following exogenous quinones by succinate and NADH was studied in mitochondria isolated from both wild type and ubiquinone (Q)-deficient strains of yeast: ubiquinone-0 (Q0), ubiquinone-1 (Q1), ubiquinone-2 (Q2), and its decyl analogue 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinone (DB), duroquinone (DQ), menadione (MQ), vitamin K1 (2-methyl-3-phytyl-1,4-naphthoquinone), the plastoquinone analogue 2,3,6-trimethyl-1,4-benzoquinone (PQOc1), plastoquinone-2 (PQ2), and its decyl analogue (2,3-dimethyl-6-decyl-1,4-benzoquinone). Reduction of the small quinones DQ, Q0, Q1, and PQOc1 by NADH occurred in both wild type and Q-deficient mitochondria in a reaction inhibited more than 50% by myxothiazol and less than 20% by antimycin. The reduction of these small quinones by succinate also occurred in wild type mitochondria in a reaction inhibited more than 50% by antimycin but did not occur in Q-deficient mitochondria suggesting that endogenous Q6 is involved in their reduction. In addition, the inhibitory effects of antimycin and myxothiazol, specific inhibitors of the cytochrome b-c1 complex, on the reduction of these small quinones suggest the involvement of this complex in the electron transfer reaction. By contrast, the reduction of Q2 and DB by succinate was insensitive to inhibitors and by NADH was 20-30% inhibited by myxothiazol suggesting that these analogues are directly reduced by the primary dehydrogenases. The dependence of the sensitivity to the inhibitors on the substrate used suggests that succinate-ubiquinone oxidoreductase interacts specifically with center i (the antimycin-sensitive site) and NADH ubiquinone oxidoreductase preferentially with center o (the myxothiazol-sensitive site) of the cytochrome b-c1 complex. The NADH dehydrogenase involved in the myxothiazol-sensitive quinone reduction faces the matrix side of the inner membrane suggesting that center o may be localized within the membrane at a similar depth as center i.
在从野生型和泛醌（Q）缺陷型酵母菌株中分离出的线粒体中，研究了琥珀酸和NADH对以下外源性醌的还原作用：泛醌-0（Q0）、泛醌-1（Q1）、泛醌-2（Q2）及其癸基类似物2,3-二甲氧基-5-甲基-6-癸基-1,4-苯醌（DB）、硬脂醌（DQ）、甲萘醌（MQ）、维生素K1（2-甲基-3-植基-1,4-萘醌）、质体醌类似物2,3,6-三甲基-1,4-苯醌（PQOc1）、质体醌-2（PQ2）及其癸基类似物（2,3-二甲基-6-癸基-1,4-苯醌）。在野生型和Q缺陷型线粒体中，NADH均可使小分子醌DQ、Q0、Q1和PQOc1发生还原反应，该反应被粘噻唑抑制超过50%，被抗霉素抑制小于20%。琥珀酸使这些小分子醌发生还原反应也发生在野生型线粒体中，该反应被抗霉素抑制超过50%，但在Q缺陷型线粒体中未发生，这表明内源性Q6参与了它们的还原过程。此外，细胞色素b-c1复合物的特异性抑制剂抗霉素和粘噻唑对这些小分子醌还原反应的抑制作用表明该复合物参与了电子传递反应。相比之下，琥珀酸对Q2和DB的还原作用对抑制剂不敏感，而NADH对其还原作用被粘噻唑抑制20%-30%，这表明这些类似物可被初级脱氢酶直接还原。对抑制剂敏感性对所用底物的依赖性表明，琥珀酸-泛醌氧化还原酶与细胞色素b-c1复合物的中心i（抗霉素敏感位点）特异性相互作用，而NADH-泛醌氧化还原酶优先与中心o（粘噻唑敏感位点）相互作用。参与粘噻唑敏感醌还原反应的NADH脱氢酶面向内膜的基质侧，这表明中心o可能定位在膜内与中心i相似的深度处。
