Grivennikova V G, Vinogradov A D
Biochim Biophys Acta. 1982 Dec 15;682(3):491-5. doi: 10.1016/0005-2728(82)90065-2.
A significant lag in the thenoyltrifluoroacetone (TTFA)-sensitive succinate: ubiquinone reductase activity was observed when a ubiquinone-deficient resolved preparation of the enzyme was assayed in the presence of exogenous ubiquinone-2 (Q2) and 2,6-dichlorophenolindophenol. No such lag was seen when the free radical of N,N,N',N'-tetramethyl-p-phenylenediamine (Wurster's Blue) was used as the terminal electron acceptor, or when the reduction of Q2 was directly measured. The apparent Km value for exogenous Q2 was determined in the Q2-mediated TTFA-sensitive succinate: Wurster's Blue reductase reaction. When the enzyme activity was measured directly by monitoring Q2 reduction without terminal acceptors, the time course of the reaction deviated from zero-order kinetics at Q2 concentrations which were much higher than those expected from the KQ2m value determined in the presence of Wurster's Blue. The time course of Q2 reduction fits a curve describing a competitive interrelationship between oxidized and reduced Q2 at the specific binding site. The data obtained are in agreement with the Q-pool behavior of ubiquinone in mitochondrial membranes and suggest that the rate of ubiquinone reduction by succinate is dependent on the Q/QH2 ratio.
当在存在外源性泛醌-2（Q2）和2,6-二氯酚靛酚的情况下，对缺乏泛醌的该酶的溶解制剂进行测定时，观察到硫辛酰三氟丙酮（TTFA）敏感的琥珀酸：泛醌还原酶活性存在显著滞后。当使用N，N，N'，N'-四甲基对苯二胺（沃斯特蓝）的自由基作为末端电子受体时，或者当直接测量Q2的还原时，未观察到这种滞后现象。在外源性Q2介导的TTFA敏感的琥珀酸：沃斯特蓝还原酶反应中测定了外源性Q2的表观Km值。当在没有末端受体的情况下通过监测Q2还原直接测量酶活性时，在Q2浓度下反应的时间进程偏离了零级动力学，该浓度远高于在存在沃斯特蓝的情况下测定的KQ2m值所预期的浓度。Q2还原的时间进程符合一条描述氧化型和还原型Q2在特定结合位点之间竞争相互关系的曲线。所获得的数据与线粒体膜中泛醌的Q池行为一致，并表明琥珀酸还原泛醌的速率取决于Q/QH2比率。
