Kinetic studies of multifunctional reactions catalysed by lipoamide dehydrogenase

Abstract

Lipoamide dehydrogenase from pig heart, in addition to catalyzing the reversible oxidation of dihydrolipoamide, displays various NADH-mediated activities including hydrogen transfer between nicotinamide nucleotides, electron transfer to inorganic acceptors and redox reaction of quinones. Kinetic studies of these reactions were carried out by measuring initial rate over a wide range of substrate concentrations and analyzing product inhibitions at different temperatures. Double reciprocal plots are generally nonlinear. Product inhibitions in some cases do not follow the patterns predictable from simple bisubstrate mechanisms. A kinetic scheme which consists of a random mechanism with a pingpong loop is proposed for multifunctional reactions catalyzed by lipoamide dehydrogenase.