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, have been measured. The reactions are found to be 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 (ΔE0′); ΔE0′ values may therefore be used as qualitative guides in formulating and selecting redox couples of NAD/H recycling value. On the basis of deuterium 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.