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Neuronal Glutamine Utilization: Pathways of Nitrogen Transfer tudied with [ 15 N]Glutamine
Author(s) -
Yudkoff Marc,
Zaleska Malgorzata M.,
Nissim Itzak,
Nelson David,
ErecinAska Maria
Publication year - 1989
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 - 10.1111/j.1471-4159.1989.tb07380.x
Subject(s) - glutamine , glutaminase , biochemistry , metabolism , synaptosome , glutamate receptor , amino acid , alanine , glutamic acid , glutamine synthetase , chemistry , catabolism , citric acid cycle , population , incubation , biology , in vitro , receptor , demography , sociology
Gas chromatography‐mass spectrometry was used to evaluate the metabolism of [ I5 N]glutamine in isolated rat brain synaptosomes. In the presence of 0.5 m M glutamine, synaptosomes accumulated this amino acid to a level of 25‐35 nmol/mg protein at an initial rate >9 nmol/min/mg of protein. The metabolism of [ 15 NJglutamine generated l5 N‐labelled glutamate, aspartate, and γ‐aminobutyric acid (GABA). An efflux of both [ 15 N]gIutamate and [ 15 N]aspartate from synaptosomes to the medium was observed. Enrichment of ,5 N in alanine could not be detected because of a limited pool size. Elimination of glucose from the incubation medium substantially increased the rate and amount of [ 15 N]aspartate formed. It is concluded that: (1) With 0.5 m M external glutamine, the glutaminase reaction, and not glutamine transport, determines the rate of metabolism of this amino acid. (2) The primary route of glutamine catabolism involves aspartate aminotransferase which generates 2‐oxoglutarate, a substrate for the tricarboxylic acid cycle. This reaction is greatly accelerated by the omission of glucose. (3) Glutamine has preferred access to a population of synaptosomes or to a synaptosomal compartment that generates GABA. (4) Synaptosomes maintain a constant internal level of glutamate plus aspartate of about 70‐80 nmol/mg protein. As these amino acids are produced from glutamine in excess of this value, they are released into the medium. Hence synaptosomal glutamine and glutamate metabolism are tightly regulated in an interrelated manner.