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Cited by 193Amino Acid Enzymes and MetabolismNeuroscience and Neuropharmacology ResearchSulfur Compounds in Biology

Nitrogen shuttling between neurons and glial cells during glutamate synthesis

Lieth, Erich, LaNoue, Kathryn F., Berkich, Deborah A., Xu, Baiyang, Ratz, Michael, Taylor, Charles, Hutson, Susan M.·2001·Journal of Neurochemistry
DOI 10.1046/j.1471-4159.2001.00156.x
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Abstract

The relationship between neuronal glutamate turnover, the glutamate/glutamine cycle and de novo glutamate synthesis was examined using two different model systems, freshly dissected rat retinas ex vivo and in vivo perfused rat brains. In the ex vivo rat retina, dual kinetic control of de novo glutamate synthesis by pyruvate carboxylation and transamination of α‐ketoglutarate to glutamate was demonstrated. Rate limitation at the transaminase step is likely imposed by the limited supply of amino acids which provide the α‐amino group to glutamate. Measurements of synthesis of 14 C‐glutamate and of 14 C‐glutamine from H 14 CO 3 have shown that 14 C‐amino acid synthesis increased 70% by raising medium pyruvate from 0.2 to 5 m m. The specific radioactivity of 14 C‐glutamine indicated that ∼30% of glutamine was derived from 14 CO 2 fixation. Using gabapentin, an inhibitor of the cytosolic branched‐chain aminotransferase, synthesis of 14 C‐glutamate and 14 C‐glutamine from H 14 CO 3− was inhibited by 31%. These results suggest that transamination of α‐ketoglutarate to glutamate in Müller cells is slow, the supply of branched‐chain amino acids may limit flux, and that branched‐chain amino acids are an obligatory source of the nitrogen required for optimal rates of de novo glutamate synthesis. Kinetic analysis suggests that the glutamate/glutamine cycle accounts for 15% of total neuronal glutamate turnover in the ex vivo retina. To examine the contribution of the glutamate/glutamine cycle to glutamate turnover in the whole brain in vivo, rats were infused intravenously with H 14 CO 3−. 14 C‐metabolites in brain extracts were measured to determine net incorporation of 14 CO 2 and specific radioactivity of glutamate and glutamine. The results indicate that 23% of glutamine in the brain in vivo is derived from 14 CO 2 fixation. Using published values for whole brain neuronal glutamate turnover, we calculated that the glutamate/glutamine cycle accounts for ∼60% of total neuronal turnover. Finally, differences between glutamine/glutamate cycle rates in these two model systems suggest that the cycle is closely linked to neuronal activity.

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  • BCAAs, aspartate and more recently alanine serve as potential nitrogen donors for the reaction that replenishes carbon for the TCA cycle.

    “A limiting factor in this reaction is the source of nitrogen, where the BCAAs, aspartate and more recently alanine serve as potential nitrogen donors (Hutson et al. 1998, 2001; Lieth et al. 2001; Bixel et al. 1997, 2001; Yudkoff et al. 1983, 1996; Kanamori et al. 1998).”

    From Alzheimer’s disease: Targeting the glutamatergic system (2020) · cites this paper as Lieth et al. 2001

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Authors
Lieth, E., LaNoue, K. F., Berkich, D. A., Xu, B., Ratz, M., Taylor, C., & Hutson, S. M.
Affiliations
  • Pennsylvania State University (US)
  • Wake Forest University Health Sciences (US)
Corresponding author
LaNoue, Kathryn F.
Venue
Journal of Neurochemistry
Publisher
Wiley
Published
2001-03-15
Volume
76
Issue
6
Pages
1712-1723
ISSN
  • 0022-3042 (ISSN-L)
  • 1471-4159
DOI
10.1046/j.1471-4159.2001.00156.x
OpenAlex
W1498448586
Cited by
192
References
42
Citations by year
2026: 3 · 2025: 5 · 2024: 2 · 2023: 2 · 2022: 4 · 2021: 6 · 2020: 9 · 2019: 3 · 2018: 5 · 2017: 5 · 2016: 6 · 2015: 9 · 2014: 9 · 2013: 11 · 2012: 8
FWCI
6.26
Type
journal article
Language
en
Open access
closed
Licence
onlinelibrary.wiley.com/termsAndConditions#vor (vor, 280 d)
Locations
  • Journal of Neurochemistry (publishedVersion)
  • PubMed (publishedVersion)
Funders
National Institute of Diabetes and Digestive and Kidney Diseases (DK34738)
Topics
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Biochemistry › Amino Acid Enzymes and Metabolism
  • Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Neuroscience and Neuropharmacology Research
  • Life Sciences › Biochemistry, Genetics and Molecular Biology › Biochemistry › Sulfur Compounds in Biology
Keywords
neuron-glia interactions, Müller cells, pyruvate carboxylation, branched-chain amino acids, gabapentin, glutamine synthesis, CO2 fixation, neuronal activity
MeSH terms
Animals, Astrocytes, Bicarbonates, Brain, Carbon Dioxide, Carbon Radioisotopes, Glutamine, Keto Acids, Models, Chemical, Models, Neurological, Neuroglia, Neurons, Nitrogen, Pyruvate Carboxylase, Pyruvates, Radioisotope Dilution Technique, Retina, Rats, Sprague-Dawley, Glutamic Acid, Rats

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