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Rate of Glutamate Synthesis from Leucine in Rat Brain Measured In Vivo by 15 N NMR
Author(s) -
Kanamori Keiko,
Ross Brian D.,
Kondrat Richard W.
Publication year - 1998
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1998.70031304.x
Subject(s) - in vivo , leucine , glutamate receptor , chemistry , nuclear magnetic resonance , amino acid , biochemistry , biology , physics , receptor , microbiology and biotechnology
The rate of glutamate synthesis from leucine by the branched‐chain aminotransferase was measured in rat brain in vivo at steady state. The rats were fed exclusively by intravenous infusion of a nutrient solution containing [ 15 N]leucine. The rate of glutamate synthesis from leucine, determined from the rate of increase of brain [ 15 N]glutamate measured by 15 N NMR and the 15 N enrichments of brain and blood leucine analyzed by gas chromatography‐mass spectrometry, was 0.7–1.8 µmol/g/h at a steady‐state brain leucine concentration of 0.25 µmol/g. A comparison of the observed fractional 15 N enrichments of brain leucine (0.42 ± 0.03) and glutamate (0.21 ± 0.015) showed that leucine provides ∼50% of glutamate nitrogen under our experimental condition. From the observed rate (0.7–1.8 µmol/g) and the known K m of the branched‐chain aminotransferase for leucine (1.2 m M ), the rate of glutamate synthesis from leucine at physiological brain leucine concentration (0.11 µmol/g) was estimated to be 0.35–0.9 µmol/g/h, with leucine providing ∼25% of glutamate nitrogen. The results strongly suggest that plasma leucine from dietary source, transported into the brain, is an important external source of nitrogen for replenishment of brain glutamate in vivo. Implications of the results for treatment of maple‐syrup urine disease patients with leucine‐restricted diet are discussed.