beta-Nicotinamide-alpha-adenine dinucleotide. Synthesis and properties of a coenzyme analog

It was not possible to synthesize beta-nicotinamide-alpha-adenine dinucleotide (NalphaAD) via the NAD pyrophosphorylase-catalyzed reaction of beta-nicotinamide mononucleotide and alpha-adenosine-5'-O-triphosphate. It was therefore prepared by reacting a mixture of beta-nicotinamide mononucleotide and alpha-adenosine-5'-O-monophosphate in aqueous pyridine, using N,N'-dicyclohexylcarbodiimide as condensing agent. NalphaAD can replace NAD in the lactate-dehydrogenase-catalyzed oxidation of lactate to pyruvate with LDH 4M from hog muscle as well as LDH 4H from pig heart. Km values are found to be about one order of magnitude higher for NalphaAD than for NAD. The turnover number for NalphaAD with LDH 4H is similar to that of NAD (95%), whereas it is reduced to one third (35%) in the reaction with LDH 4M. Experiments findings are discussed on the lines of a NAD-equivalent conformation of NalphaAD in the holoenzyme complex.