Nicotinamide coenzyme regeneration. The rates of some 1,4-dihydropyridine, pyridinium salt, and flavin mononucleotide hydrogen-transfer reactions

Abstract

The rates of H-transfer between various 1,4-dihydropyridines and pyridinium salts (including NADH and NAD+), and from 1,4-dihydropyridines to FMN, were measured. The reactions are sufficiently slow for H-transfer to be rate-determining to a significant extent when such systems are applied for nicotinamide coenzyme recycling purposes. The rates of H-transfer parallel the magnitudes of the donor-acceptor redox potential differences (.DELTA.E0''); .DELTA.E0'' values may therefore be used as qualitative guides in formulating and selecting redox couples of NAD/H recycling value. On the basis of 2H isotope effects, it is concluded that formation of a complex prior to H-transfer is not rate determining for 1,4-dihydropyridine-NAD+ reactions. This behavior is in contrast to that of other model alcohol dehydrogenase systems.