Role of lecithin in D-beta-hydroxybutyrate dehydrogenase function

Binding of NADH to D-β-hydroxybutyrate dehydrogenase, a lecithin-requiring enzyme from beef heart mitochondria, has been studied using a homogeneous enzyme which is soluble and, most important, free of lipid. The enzyme complexed with lecithin or with a phospholipid mixture containing lecithin binds NADH with a dissociation constant of 6–16 μM, while the apoenzyme or phospholipid alone or complexes formed with non-reactivating phospholipids bind no NADH. The results show that the binding of NADH to the dehydrogenase is dependent upon the formation of an enzyme-lecithin complex. This is the first demonstration of a role of lipid in a particular step of the reaction mechanism of a specific lipid-requiring enzyme.