title: Location of deuterium oxide solvent isotope effects in the glutamate dehydrogenase reaction.
abstract: Stopped flow studies of D2O kinetic solvent isotope effects on the reaction catalyzed by L-glutamate dehydrogenase reveal, in addition to several effects apparently attributable simply to pKa shifts, a 2-fold pH-independent effect on the velocity of the steady state oxidative deamination of L-glutamate by enzyme and NADP. Comparable pH-independent D2O kinetic solvent isotope effects are seen both in a transient phase of the reaction in which alpha-ketoglutarate is displaced by L-glutamate from an enzyme-NADPH-alpha-ketoglutarate (product) complex and in an analogous model reaction in which alpha-ketoglutarate is displaced by D-glutamate. These results suggest that alpha-ketoglutarate dissociation from an enzyme-NADPH-alpha-ketoglutarate complex is rate-limiting in the steady state.
mesh_terms: D003903:Deuterium; D005969:Glutamate Dehydrogenase / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007656:Ketoglutaric Acids / Q000378:metabolism; D007700:Kinetics; D009249:NADP / Q000378:metabolism
chemical_list: D007656:Ketoglutaric Acids; D009249:NADP; D003903:Deuterium; D005969:Glutamate Dehydrogenase