β-Nicotinamide-α-Adenine Dinucleotide. Synthesis and Properties of a Coenzyme Analog

Abstract
It was not possible to synthesize .beta.-nicotinamide-.alpha.-adenine dinucleotide (N.alpha.AD) via the NAD pyrophosphorylase[EC 2.7.7.1]-catalyzed reaction of .beta.-NMN and .alpha.-ATP. It was therefore prepared by reacting a mixture of .beta.-NMN and .alpha.-AMP in aqueous pyridine, using N,N''-dicyclohexylcarbodiimide as condensing agent. N.alpha.AD+ can replace NAD+ in the lactate-dehydrogenase[LDH-EC 1.1.1.27]-catalyzed oxidation of lactate to pyruvate with LDH 4M from hog muscle and LDH 4H from pig heart. Km values are about one order of magnitude higher for N.alpha.AD+ than for NAD+. The turnover number for N.alpha.AD+ with LDH 4H is similar to that of NAD+ (95%), but it is reduced to 1/3 (35%) in the reaction with LDH 4M. Experimental findings are discussed on the lines of a NAD+-equivalent conformation of N.alpha.AD+ in the holoenzyme complex.