Bunik V, Follmann H, Bisswanger H
A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russia.
Biol Chem. 1997 Oct;378(10):1125-30. doi: 10.1515/bchm.1997.378.10.1125.
The regulation of mitochondrial dehydrogenases of 2-oxoacids by thioredoxin is established. It is found that at low NAD+ and saturating concentrations of 2-oxoacids and CoA, inactivation of 2-oxoacid dehydrogenase complexes takes place, preventing NAD+ reduction under such conditions. However, addition of oxidized E. coli thioredoxin to the reaction medium without dithiothreitol allows effective NAD+ reduction at this substrate ratio. Product accumulation curves show that thioredoxin activates the complexes by protecting them from the inactivation observed in the conditions when the complex-bound dihydrolipoate is accumulated. Disappearance of the activatory effect of thioredoxin after its treatment with SH-specific reagents indicates the involvement of the redox-active cysteine couple of thioredoxin in its activation of 2-oxoacid dehydrogenase complexes. The redox-inactive thioredoxin not only shows no activation, but in fact exerts an inhibitory effect. The inhibition manifests the complex formation between SH-modified thioredoxin and dehydrogenase systems, involving amino acid residues of thioredoxin other than cysteine. High efficiency of thioredoxin from E. coli as compared to chloroplast thioredoxin f and glutathione disulfide is revealed. This indicates the importance of specific protein structure also for the influence of the redox-active thioredoxin upon the 2-oxoacid dehydrogenase complexes. The results obtained suggest that these key enzyme systems of mitochondrial metabolism represent previously unidentified targets for the action of mitochondrial thioredoxin, which is known to resemble the E. coli counterpart studies in this work.
硫氧还蛋白对2-氧代酸线粒体脱氢酶的调节作用已得到证实。研究发现，在低NAD⁺以及2-氧代酸和辅酶A饱和浓度的情况下，2-氧代酸脱氢酶复合物会失活，从而在这种条件下阻止NAD⁺的还原。然而，在没有二硫苏糖醇的反应介质中加入氧化型大肠杆菌硫氧还蛋白，能在这种底物比例下实现有效的NAD⁺还原。产物积累曲线表明，硫氧还蛋白通过保护复合物免受因复合物结合的二氢硫辛酸积累而导致的失活作用，从而激活这些复合物。硫氧还蛋白经SH特异性试剂处理后其激活作用消失，这表明硫氧还蛋白具有氧化还原活性的半胱氨酸对在激活2-氧代酸脱氢酶复合物过程中发挥了作用。无氧化还原活性的硫氧还蛋白不仅没有激活作用，实际上还发挥了抑制作用。这种抑制作用表现为SH修饰的硫氧还蛋白与脱氢酶系统之间形成复合物，涉及硫氧还蛋白中除半胱氨酸以外的氨基酸残基与脱氢酶系统的结合作用。与叶绿体硫氧还蛋白f和谷胱甘肽二硫化物相比，大肠杆菌硫氧还蛋白具有更高的效率。这表明特定的蛋白质结构对于具有氧化还原活性的硫氧还蛋白对2-氧代酸脱氢酶复合物的影响同样重要性作用。所获得的结果表明，线粒体代谢的这些关键酶系统代表了线粒体硫氧还蛋白作用以前未被识别出作用靶点对象作用，而在本研究工作已知线粒体硫氧还蛋白类似于大肠杆菌中的对应物。 （注：原文最后一句翻译稍显复杂，尽力贴近原文结构但译文可能稍显拗口，可根据实际情况调整表述使其更通顺）
