O'Connor T P, Roche T E, Paukstelis J V
J Biol Chem. 1982 Mar 25;257(6):3110-2.
The dihydrolipoyl transacetylase component of the pyruvate dehydrogenase complex catalyzes a reversible reaction between acetyl-CoA and dihydrolipoamide that results in the formation of S-acetyldihydrolipoamide. We have used 13C nuclear magnetic resonance to investigate this reaction using exogenous forms of dihydrolipoamide in place of the protein-bound substrate. With substrate levels of dihydrolipoamide and enzymatically generated [1-13C]acetyl-CoA, both 6-S-[1-13C]acetyl- and 8-S-[1-13C]acetyldihydrolipoamide were formed in the transacetylation reaction and both species participated in the reverse reaction to yield [1-13C]acetyl-CoA and free dihydrolipoamide. The 8-S-acetyl derivative was the principal product. It is suggested that acetylation of both the 6- and 8-thiols of dihydrolipoamide results as a consequence of intramolecular migration following acetylation at a single site. After longer periods of reaction, some 6,8-S,S-[1-13C]diacetyldihydrolipoamide also accumulated. We have also found that [1-13C]acetyl-CoA reacts slowly with dihydrolipoamide in a nonenzymatic reaction to yield the two monoacetylated and some diacetylated derivative. In the reverse reaction catalyzed by the dihydrolipoyl transacetylase, it was clear that monoacetyl derivatives were depleted much more rapidly than the diacetyl derivatives, although we could not quantitate the change in the low concentration of the diacetyl derivative.
丙酮酸脱氢酶复合体的二氢硫辛酰转乙酰酶组分催化乙酰辅酶A与二氢硫辛酰胺之间的可逆反应，生成S - 乙酰二氢硫辛酰胺。我们利用13C核磁共振技术，使用外源性二氢硫辛酰胺替代与蛋白质结合的底物来研究此反应。在二氢硫辛酰胺和酶促生成的[1 - 13C]乙酰辅酶A的底物水平下，转乙酰化反应中生成了6 - S - [1 - 13C]乙酰基 - 和8 - S - [1 - 13C]乙酰基二氢硫辛酰胺，且这两种物质都参与了逆反应，生成[1 - 13C]乙酰辅酶A和游离的二氢硫辛酰胺。8 - S - 乙酰基衍生物是主要产物。这表明二氢硫辛酰胺的6 - 和8 - 硫醇基团的乙酰化是由于在单个位点乙酰化后分子内迁移的结果。反应较长时间后，一些6,8 - S,S - [1 - 13C]二乙酰基二氢硫辛酰胺也会积累。我们还发现，[1 - 13C]乙酰辅酶A在非酶促反应中与二氢硫辛酰胺反应缓慢，生成两种单乙酰化产物和一些二乙酰化衍生物。在二氢硫辛酰转乙酰酶催化的逆反应中，很明显单乙酰化衍生物的消耗速度比二乙酰化衍生物快得多，尽管我们无法对低浓度二乙酰化衍生物的变化进行定量。
