Storey B T
Johnson Research Foundation, University of Pennsylvania, Philadelphia, Pennsylvania 19104.
Plant Physiol. 1972 Mar;49(3):314-22. doi: 10.1104/pp.49.3.314.
The cytochromes c of mung bean (Phaseolus aureus) mitochondria become reduced when sulfide, a cytochrome oxidase inhibitor free from uncoupling side effects, is added to the aerobic mitochondrial suspension in the absence of added substrate. The cytochromes b remain largely oxidized. Subsequent addition of ATP results in partial oxidation of the cytochromes c and partial reduction of the cytochromes b due to ATP-driven reverse electron transport through the second site of energy conservation, or coupling site, of the respiratory chain. Cytochrome a is also oxidized under these conditions, but there is no concomitant reduction of the flavoprotein components, of ubiquinone, or of endogenous pyridine nucleotide. The reaction is abolished by oligomycin. The reducing equivalents transported from the cytochromes c and a in ATP-driven reverse electron transport are about 2-fold greater than those which appear in the cytochromes b. It is suggested that the equivalents not accounted for are present in a coupling site enzyme at the second site of energy conservation which interacts with the respiratory chain carriers by means of the dithiol-disulfide couple; this couple would not show absorbance changes with redox state over the wavelength range examined. With succinate present, reverse electron transport can be demonstrated at both coupling sites in both the aerobic steady state and in anaerobiosis. ATP-driven reverse electron transport in anaerobiosis maintains cytochrome a 30% oxidized while endogenous pyridine nucleotide is 50% reduced.When mung bean mitochondria, oxidizing succinate in the presence of sulfide through the alternate, cyanide- and sulfide-insensitive terminal oxidase, become anaerobic, cytochrome b(557), which has remained largely oxidized, becomes slowly reduced. The slow reduction is observed in coupled, energized mitochondria and in uncoupled mitochondria; the time course parallels the reduction of cytochrome a(3) under the same conditions. It appears that sulfide-liganded, oxidized cytochrome a(3) may be in close enough proximity to cytochrome b(557) in the membrane to inhibit the reduction of the latter.
当在没有添加底物的情况下，将一种无解偶联副作用的细胞色素氧化酶抑制剂硫化物添加到需氧线粒体悬浮液中时，绿豆（Phaseolus aureus）线粒体的细胞色素c会被还原。细胞色素b大部分仍保持氧化状态。随后添加ATP会导致细胞色素c部分氧化，细胞色素b部分还原，这是由于ATP驱动的反向电子传递通过呼吸链能量守恒的第二个位点，即偶联位点。在这些条件下，细胞色素a也会被氧化，但黄素蛋白组分、泛醌或内源性吡啶核苷酸不会伴随还原。该反应被寡霉素消除。在ATP驱动的反向电子传递中，从细胞色素c和a转运的还原当量比出现在细胞色素b中的还原当量大约大2倍。有人认为，未被解释的当量存在于能量守恒第二个位点的偶联位点酶中，该酶通过二硫醇 - 二硫化物偶联与呼吸链载体相互作用；在检测的波长范围内，这种偶联不会随氧化还原状态显示吸光度变化。存在琥珀酸时，在需氧稳定状态和厌氧状态下，两个偶联位点均可证明有反向电子传递。厌氧状态下ATP驱动的反向电子传递使细胞色素a保持30%的氧化状态，而内源性吡啶核苷酸有50%被还原。当绿豆线粒体在硫化物存在下通过交替的、对氰化物和硫化物不敏感的末端氧化酶氧化琥珀酸时变为厌氧状态，大部分保持氧化状态的细胞色素b(557)会缓慢还原。在偶联的、有能量的线粒体和未偶联的线粒体中均观察到这种缓慢还原；时间进程与相同条件下细胞色素a(3)的还原情况平行。似乎膜中与硫化物结合的氧化型细胞色素a(3)可能与细胞色素b(557)靠得足够近，从而抑制后者的还原。
