Interactions of lipoyl domains with the E1p subunits of the pyruvate dehydrogenase multienzyme complex from Escherichiacoli

Abstract

Equilibrium binding experiments were carried out with lipoyl domains and the pyruvate decarboxylase [pyruvate dehydrogenase (lipoamide), Elp, EC 1.2.4.1)] component of the pyruvate dehydrogenase multienzyme complex of Escherichia coli. The dissociation constant (K _s) was estimated to be not less than 0.3 mM, exceeding the K _m value (33 μM) 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 Elp. The difference between K _s and K _m suggests that the formation and release of reductively acetylated lipoyl domains from the enzyme may be a relatively rapid step in the mechanism.