Butterworth P J, Tsai C S, Eley M H, Roche T E, Reed L J
J Biol Chem. 1975 Mar 10;250(5):1921-5.
The mammalian pyruvate dehydrogenase complex contains a core, consisting of dihydrolipoyl transacetylase, to which pyruvate dehydrogenase and dihydrolipoyl dehydrogenase are joined. This report describes studies on the kinetic mechanism of the transacetylase-catalyzed reaction between [1-14C]acetyl-CoA and dihydrolipoamide. This reaction appears to be a model of the physiological reaction, in which the acetyl group is transferred from the S-acetyldihydrolipoyl moiety, bound covalently to the transacetylase, to CoA. The model reaction is not affected by pyruvate dehydrogenase or dihydrolipoyl dehydrogenase, their substrates and products, or by removal of the covalently bound lipoyl moiety. These findings, together with the results of initial velocity, product inhibition, and dead-end inhibition studies, indicate that the model reaction and, apparently, the physiological reaction as well, proceeds via the Random Bi Bi (rapid equilibrium) mechanism. It appears that at the catalytic center of the transacetylase there are two adjacent sites, one that binds CoA and acetyl-CoA and another that binds dihydrolipoamide and S-acetyldihydrolipoamide (or the corresponding forms of the covalently bound lipoyl moiety.
哺乳动物丙酮酸脱氢酶复合体含有一个核心，由二氢硫辛酰胺转乙酰酶组成，丙酮酸脱氢酶和二氢硫辛酰胺脱氢酶与之相连。本报告描述了关于转乙酰酶催化的[1-14C]乙酰辅酶A与二氢硫辛酰胺之间反应的动力学机制的研究。该反应似乎是生理反应的一个模型，其中乙酰基从共价结合在转乙酰酶上的S-乙酰二氢硫辛酰胺部分转移到辅酶A。模型反应不受丙酮酸脱氢酶或二氢硫辛酰胺脱氢酶、它们的底物和产物的影响，也不受去除共价结合的硫辛酰胺部分的影响。这些发现，连同初速度、产物抑制和终产物抑制研究的结果，表明模型反应以及显然生理反应也是通过随机双底物双产物（快速平衡）机制进行的。似乎在转乙酰酶的催化中心有两个相邻位点，一个结合辅酶A和乙酰辅酶A，另一个结合二氢硫辛酰胺和S-乙酰二氢硫辛酰胺（或共价结合的硫辛酰胺部分的相应形式）。
