EFFECT OF SUBSTITUENTS OF THE BENZOQUINONE RING ON ELECTRON-TRANSFER ACTIVITIES OF UBIQUINONE DERIVATIVES
EFFECT OF SUBSTITUENTS OF THE BENZOQUINONE RING ON ELECTRON-TRANSFER ACTIVITIES OF UBIQUINONE DERIVATIVES
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DOI：
10.1016/0005-2728(90)90082-f
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发表时间：
1990-02-22
期刊：
影响因子：
--
通讯作者：
YU, CA
中科院分区：
文献类型：
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作者：
GU, LQ;YU, L;YU, CA
采用6位具有癸基（或香叶基）侧链且苯醌环2、3和5位具有不同排列的甲基、甲氧基和氢的合成泛醌衍生物，研究了泛醌1,4-苯醌环上的取代基对其在牛心线粒体琥珀酸细胞色素c还原酶区电子转移活性的影响。使用琥珀酸泛醌还原酶和琥珀酸细胞色素 c 还原酶测量琥珀酸对醌衍生物的还原。使用泛醇-细胞色素 c 还原酶测量对苯二酚衍生物的氧化。将醌衍生物的电子转移效率与2,3-二甲氧基-5-甲基-6-癸基-1,4-苯醌进行比较。当醌衍生物用作琥珀酸泛醌还原酶的电子受体时，5位上的甲基不如2位和3位上的甲氧基重要。用氢取代 5-甲基会导致活性略有增加。然而，用甲基取代2-和3-甲氧基之一或两者会完全消除电子受体活性。用氢取代3-甲氧基会导致电子受体活性完全丧失，而用氢取代2-甲氧基会导致活性降低70%，这表明3位甲氧基比2位甲氧基更具特异性。被泛醇-细胞色素c还原酶氧化的对苯二酚衍生物的结构要求不太严格。当用作泛醇-细胞色素 c 还原酶的电子供体时，所有检查的 1,4-苯醌衍生物均显示出部分活性。在 2、3 或 5 位具有未取代位置且在 6 位具有癸基的衍生物在高浓度下表现出底物抑制作用。当使用完全取代的衍生物时，没有观察到这种底物抑制。琥珀酸-细胞色素 c 还原酶还原醌衍生物的结构要求不如琥珀酸-泛醌还原酶那么具体。用甲基取代 2- 和 3- 甲氧基之一或两者并保持 5-位未取代（质体醌衍生物），产生对琥珀酸-Q 还原酶没有受体活性的衍生物。然而，这些衍生物在琥珀酸-细胞色素 c 还原酶存在下可被琥珀酸还原。这种还原反应是抗霉素敏感的，需要内源性泛醌，表明这些（质体醌）衍生物只能接受来自泛醇-细胞色素 c 还原酶 Qi 位点的泛半醌自由基的电子，而不能接受来自琥珀酸-泛醌还原酶 QP 的电子。
The effect of substituents on the 1,4-benzoquinone ring of ubiquinone on its electron-transfer activity in the bovine heart mitochondrial succinate-cytochrome c reductase region is studied by using synthetic ubiquinone derivatives that have a decyl (or geranyl) side-chain at the 6-position and various arrangements of methyl, methoxy and hydrogen in the 2, 3 and 5 positions of the benzoquinone ring. The reduction of quinone derivatives by succinate is measured with succinate-ubiquinone reductase and with succinate-cytochrome c reductase. Oxidation of quinol derivatives is measured with ubiquinol-cytochrome c reductase. The electron-transfer efficacy of quinone derivatives is compared to that of 2,3-dimethoxy-5-methyl-6-decyl-1,4-benzoquinone. When quinone derivatives are used as the electron acceptor for succinate-ubiquinone reductase, the methyl group at the 5-position is less important than are the methoxy groups at the 2- and 3-positions. Replacing the 5-methyl group with hydrogen causes a slight increase in activity. However, replacing one or both of 2- and 3-methoxy groups with a methyl completely abolishes electron-acceptor activity. Replacing the 3-methoxy group with hydrogen results in a complete loss of electron-acceptor activity, while replacing the 2-methoxy with hydrogen results in an activity decrease by 70%, suggesting that the methoxy group at the 3-position is more specific than that at the 2-position. The structural requirements for quinol derivatives to be oxidized by ubiquinol-cytochrome c reductase are less strict. All 1,4-benzoquinol derivatives examined show partial activity when used as electron donors for ubiquinol-cytochrome c reductase. Derivatives that possess on unsubstituted position at 2, 3 or 5, with a decyl group at the 6-position, show substrate inhibition at high concentrations. Such substrate inhibition is not observed when fully substituted derivatives are used. The structural requirements for quinone derivatives to be reduced by succinate-cytochrome c reductase are less specific than those for succinate-ubiquinone reductase. Replacing one or both of the 2- and 3-methoxy groups with a methyl and keeping the 5-position unsubstituted (plastoquinone derivatives) yields derivatives with no acceptor activity for succinate-Q reductase. However, these derivatives are reducible by succinate in the presence of succinate-cytochrome c reductase. This reduction is antimycin-sensitive and requires endogenous ubiquinone, suggesting that these (plastoquinone) derivatives can only accept electrons from the ubisemiquinone radical at the Qi site of ubiquinol-cytochrome c reductase, and cannot accept electrons from the QPs of succinate-ubiquinone reductase.