Graham L D, Perham R N
Department of Biochemistry, University of Cambridge, England.
FEBS Lett. 1990 Mar 26;262(2):241-4. doi: 10.1016/0014-5793(90)80200-3.
Equilibrium binding experiments were carried out with lipoyl domains and the pyruvate decarboxylase [pyruvate dehydrogenase (lipoamide), E1p, EC 1.2.4.1)] component of the pyruvate dehydrogenase multienzyme complex of Escherichia coli. The dissociation constant (Ks) was estimated to be not less than 0.3 mM, exceeding the Km value (33 microM) for reductive acetylation of the domains by an order of magnitude. Thus, the lipoyl domain, which is required to promote reductive acetylation of the lipoyl group, does not appear to do this simply by enhancing the binding to E1p. The difference between Ks and Km suggests that the formation and release of reductively acetylated lipoyl domains from the enzyme may be a relatively rapid step in the mechanism.
利用硫辛酰结构域与大肠杆菌丙酮酸脱氢酶多酶复合体的丙酮酸脱羧酶[丙酮酸脱氢酶（硫辛酰胺），E1p，EC 1.2.4.1]组分进行了平衡结合实验。解离常数（Ks）估计不小于0.3 mM，比这些结构域进行还原乙酰化反应的Km值（33 microM）高出一个数量级。因此，促进硫辛酰基团还原乙酰化所必需的硫辛酰结构域，似乎并非仅仅通过增强与E1p的结合来实现这一作用。Ks与Km之间的差异表明，还原乙酰化的硫辛酰结构域在酶上的形成和释放可能是该机制中一个相对快速的步骤。
