Effect of cofactors, oestrogens and magnesium ions on the activity and stability of human glutamate dehydrogenase

Publisher Website
Google Scholar
Abstract
The stability of crystalline human-liver glutamate dehydrogenase and purified human-uterine glutamate dehydrogenase is markedly decreased by NADPH at physiological concentrations. This effect is potentiated by diethylstilboestrol and associated with an increase in titratable thiol groups. Magnesium ions at intracellular concentrations protect the enzyme (both human and ox) against the NADPH-, NADH- and diethylstilboestrol-induced instability; protection is almost nil at extracellular concentrations. Magnesium ions affect the velocity with NAD+, NADH and NADPH but not with NADP+. They change apparent equilibrium and cofactor dissociation constants but not the number of binding sites. In a buffer resembling intracellular fluid, the stability of human-liver and -uterine glutamate dehydrogenase at physiological concentrations is not significantly affected by 10/iM-oestradiol-17[beta],-dehydroepiandrosterone, -testosterone, -progesterone or -cortisol. Even in the presence of physiological concentrations of NADPH, natural steroids exert only minimal effects not comparable with those of diethylstilboestrol.