Lipoamide dehydrogenase is a component of the glycine cleavage system as well as of the alpha-ketoacid dehydrogenase complexes (By similarity). This enzyme has lipoamide dehydrogenase activity and NADH -> NAD transhydrogenation activity. Also displays some NADH-ferricyanide reductase and NADPH -> NAD transydrogenation activities. (R)-N(6)-dihydrolipoyl-L-lysyl-[protein] + NAD(+) = (R)-N(6)-lipoyl-L-lysyl-[protein] + H(+) + NADH Binds 1 FAD per subunit. Lipoamide reduction and the NADH -> NAD reaction are both completely inhibited by copper and cadmium ions. Optimum pH is 7.5 for NADH -> NAD transhydrogenation, 6.5 for lipoamide reduction, 4.5 for NADPH -> NAD transhydrogenation, and 6.5 for NADH-ferricyanide reduction. Homodimer. The active site is a redox-active disulfide bond. Belongs to the class-I pyridine nucleotide-disulfide oxidoreductase family.