Location of deuterium oxide solvent isotope effects in the glutamate dehydrogenase reaction

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-glutam...

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Bibliographic Details
Published in:The Journal of biological chemistry 1975-07, Vol.250 (13), p.5243-5246
Main Authors: Colen, A H, Wilkinson, R R, Fisher, H F
Format: Article
Language:English
Subjects:
Deuterium
Glutamate Dehydrogenase - metabolism
Hydrogen-Ion Concentration
Ketoglutaric Acids - metabolism
Kinetics
NADP - metabolism
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Summary: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.
ISSN:0021-9258
1083-351X
DOI:10.1016/S0021-9258(19)41302-1