Regulation of coenzyme utilization by the dual nucleotide-specific glucose 6-phosphate dehydrogenase from Leuconostoc mesenteroids

Abstract

The dual wavelength assay technique (H. R. Levy, and G. H. Daouk, 1979, J. Biol. Chem. 254, 4843–4847) is used to examine the rates of the NADP- and NAD-linked reactions of Leuconostoc mesenteroides glucose 6-phosphate dehydrogenase simultaneously under various conditions. Inhibition by ATP, MgATP 2−, acetyl-CoA, and palmitoyl-CoA is greatly diminished at high glucose 6- P concentration which favors the NAD-linked reaction. Increasing NADPH NADP + concentration ratios inhibit the NADP-linked, but stimulate the NAD-linked reaction. The selective effects of glucose 6- P and the NADPH NADP + concentration ratio, which cannot be detected by conventional assays, are explained in terms of the differing kinetic mechanisms for the NADP-linked and NAD-linked reactions previously described (C. Olive, M. E. Geroch, and H. R. Levy, 1971, J. Biol. Chem. 246, 2047–2057) . It is proposed that these effects constitute the mechanism whereby the nucleotide specificity of the amphibolic glucose 6-phosphate dehydrogenase from Leuconostoc mesenteroides is regulated.