Lipoamide dehydrogenase is an essential component of the pyruvate dehydrogenase (PDH) and 2-oxoglutarate dehydrogenase (ODH) complexes. Catalyzes the reoxidation of dihydrolipoyl groups which are covalently attached to the lipoate acyltransferase components (E2) of the complexes. Also catalyzes a reversible NADH:NAD(+) transhydrogenation, and is able to transfer electrons from NADH to various redox-active compounds and quinones. May be involved in quinone redox cycling in C.glutamicum. (R)-N(6)-dihydrolipoyl-L-lysyl-[protein] + NAD(+) = (R)-N(6)-lipoyl-L-lysyl-[protein] + H(+) + NADH Binds 1 FAD per subunit. Optimum pH is 7.0-7.5 for the reduction of lipoate by NADH. Optimum temperature is 50 degrees Celsius for the reduction of lipoate by NADH. Carbohydrate metabolism; tricarboxylic acid cycle; succinyl-CoA from 2-oxoglutarate (dehydrogenase route): step 1/1. Homodimer (By similarity). Part of an unusual ODH/PDH supercomplex, consisting of AceE (E1), AceF (E2), and Lpd (E3) together with OdhA (E1+E2). The active site is a redox-active disulfide bond. Overexpression of LPD enhances sensitivity to menadione, but has no effect on sensitivity to paraquat or hydrogen peroxide. Belongs to the class-I pyridine nucleotide-disulfide oxidoreductase family.