Bunik V, Shoubnikova A, Loeffelhardt S, Bisswanger H, Borbe H O, Follmann H
A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russian Federation.
FEBS Lett. 1995 Sep 4;371(2):167-70. doi: 10.1016/0014-5793(95)00904-n.
The thioredoxin-catalyzed insulin reduction by dihydrolipoate was applied to study the 2-oxoacid: lipoate oxidoreductase activity of 2-oxoacid dehydrogenase complexes. The enzymatic and non-enzymatic mechanisms of the transfer of reducing equivalents from the complexes to free lipoic acid (alpha-lipoic acid, 6,8-thiooctic acid) were distinguished using the high stereoselectivity of the complex enzymes to the R-enantiomer of lipoate. Unlike these enzymes, thioredoxin from E. coli exhibited no stereoselectivity upon reduction with chemically obtained dihydrolipoate. However, coupled to the dihydrolipoate production by the dehydrogenase complexes, the process was essentially sensitive both to the enantiomer used and the dihydrolipoyl dehydrogenase activity of the complexes. These results indicated the involvement of the third complex component, dihydrolipoyl dehydrogenase, in the 2-oxoacid-dependent dihydrolipoate formation. The implication of the investigated reaction for a connection between thioredoxin and the 2-oxoacid dehydrogenase complexes in the mitochondrial metabolism are discussed.
硫氧还蛋白催化的二氢硫辛酸还原胰岛素被用于研究2-氧代酸脱氢酶复合物的2-氧代酸：硫辛酸氧化还原酶活性。利用复合酶对硫辛酸R-对映体的高立体选择性，区分了复合物向游离硫辛酸（α-硫辛酸，6,8-硫辛酸）转移还原当量的酶促和非酶促机制。与这些酶不同，用化学方法获得的二氢硫辛酸还原时，来自大肠杆菌的硫氧还蛋白没有表现出立体选择性。然而，与脱氢酶复合物产生二氢硫辛酸相偶联时，该过程对所使用的对映体和复合物的二氢硫辛酰胺脱氢酶活性都基本敏感。这些结果表明，复合物的第三个组分二氢硫辛酰胺脱氢酶参与了2-氧代酸依赖性二氢硫辛酸的形成。讨论了所研究反应对于硫氧还蛋白与线粒体代谢中2-氧代酸脱氢酶复合物之间联系的意义。
