title: Steady-state in vivo glutamate dehydrogenase activity in rat brain measured by 15N NMR.
abstract: The in vivo activity of glutamate dehydrogenase (GDH) in the direction of reductive amination was measured in rat brain at steady-state concentrations of brain ammonia and glutamate after intravenous infusion of the substrate 15NH4+. The in vivo rate was determined from the steady-state fractional 15N enrichment of brain ammonia, measured by selective observation of 15NH4+ protons in brain extract by 1H-15N heteronuclear multiple-quantum coherence transfer NMR, and the rate of increase of brain [15N]glutamate and [2-15N]glutamine measured by 15N NMR. The in vivo GDH activity was 0.76-1.17 mumol/h/g, and 1.1-1.2 mumol/h/g at 1.0 +/- 0.17 mumol/g. Comparison of the observed in vivo GDH activity with the in vivo rates of glutamine synthesis and of phosphate-activated glutaminase suggests that, under mild hyperammonemia, GDH-catalyzed de novo synthesis can provide a minimum of 19% of the glutamate pool that is recycled from neurons to astrocytes through the glutamate-glutamine cycle.
authors.affiliation: Magnetic Resonance Spectroscopy Laboratory, Huntington Medical Research Institutes, Pasadena, California 91105, USA.
authors.forename: K
authors.initials: K
authors.lastname: Kanamori
authors.forename: B D
authors.initials: BD
authors.lastname: Ross
mesh_terms: D000641:Ammonia / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000201:enzymology*; D005969:Glutamate Dehydrogenase / Q000378:metabolism*; D018698:Glutamic Acid / Q000096:biosynthesis; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D051381:Rats; D017208:Rats, Wistar
chemical_list: D018698:Glutamic Acid; D000641:Ammonia; D005969:Glutamate Dehydrogenase