Glutamin: the pathway in the body

Glutamin is part of the pathway “GABA, glutamate and glutamine”. This page shows the whole pathway; the station of Glutamin is highlighted.

Where this laboratory value sits: Glutamine — amino acid from astrocytes. Glutamine is the form in which the brain's support cells (astrocytes) resupply nerve cells. It carries no electrical charge and is easily moved across membranes. Source 1, 2

In brief

Glutamate and GABA are messengers of the nervous system: glutamate excites, GABA inhibits. Nerve cells make GABA from glutamate, and astrocytes resupply both via glutamine.

The pathway step by step

1. Glutamine → Glutamate Glutaminase The enzyme glutaminase removes an amino group from glutamine, forming glutamate, the brain's main excitatory messenger. Source 1, 4
2. Glutamate → GABA GAD65, GAD67 · Vitamin B6 (PLP) In certain nerve cells, glutamate decarboxylase (GAD65, GAD67) removes a carboxyl group from glutamate, forming GABA, the main inhibitory messenger. The enzyme needs pyridoxal phosphate, the active form of vitamin B6. Source 3, 2
3. GABA → Synaptic cleft · VGAT, VGLUT (vesicle) Vesicular transporters load GABA and glutamate into storage vesicles. On a signal, the cells release the contents into the gap between two nerve cells, where they bind to receptors. Source 1, 2
4. In the astrocyte → Glutamine (astrocyte) Glutamine synthetase · ATP, Ammonia Glutamine synthetase adds an amino group from ammonia to glutamate, using up ATP. The astrocyte passes the glutamine back to the nerve cell, closing the cycle. Source 1, 4
5. In the astrocyte → Succinic semialdehyde GABA transaminase · Vitamin B6 (PLP), α-Ketoglutarate GABA transaminase transfers the amino group of GABA to α-ketoglutarate. This yields succinic semialdehyde and glutamate. This enzyme also works with pyridoxal phosphate. Source 4, 1
6. Succinic semialdehyde → Succinate SSADH · NAD⁺ Succinic semialdehyde dehydrogenase turns it into succinate, an intermediate of the citric acid cycle. Via this shunt, GABA flows back into energy metabolism. Source 4, 2

Cofactors in this pathway

• Vitamin B6 (PLP) — Cofactor of glutamate decarboxylase, which forms GABA, and of GABA transaminase Source 3, 4In the ORY catalogue as a laboratory value: Vitamin B6
• Magnesium — Metal ion and part of Mg-ATP at the active site of glutamine synthetase Source 7In the ORY catalogue as a laboratory value: Magnesium
• α-Ketoglutarate — Accepts the amino group from GABA at GABA transaminase Source 4, 1In the ORY catalogue as a laboratory value: Alpha-Ketoglutarat (2-Oxoglutarat)
• NAD⁺ — Accepts hydrogen when SSADH converts succinic semialdehyde to succinate Source 4In the ORY catalogue as a laboratory value: NAD⁺ (Nicotinamidadenindinukleotid)
• Sodium — The transporters EAAT1 and EAAT2 carry glutamate into the astrocyte together with sodium Source 5In the ORY catalogue as a laboratory value: Natrium (intrazellulär)
• Potassium — Moved out of the cell in exchange during glutamate transport via EAAT Source 5In the ORY catalogue as a laboratory value: Kalium (intrazellulär)

What acts on this pathway

• Vigabatrin — Vigabatrin binds irreversibly to GABA transaminase. The prescribing information states that GABA is therefore broken down more slowly and is present in higher amounts in the nervous system. Source 6

Sources

1. Bak LK, Schousboe A, Waagepetersen HS. The glutamate/GABA-glutamine cycle: aspects of transport, neurotransmitter homeostasis and ammonia transfer. J Neurochem 2006 · PubMed 16787421
2. Andersen JV, Schousboe A et al. Milestone Review: Metabolic dynamics of glutamate and GABA mediated neurotransmission - The essential roles of astrocytes. J Neurochem 2023 · PubMed 36919769
3. Martin DL, Rimvall K. Regulation of gamma-aminobutyric acid synthesis in the brain. J Neurochem 1993 · PubMed 8419527
4. Waagepetersen HS, Sonnewald U, Schousboe A. Compartmentation of glutamine, glutamate, and GABA metabolism in neurons and astrocytes: functional implications. Neuroscientist 2003 · PubMed 14580123
5. Danbolt NC. Glutamate uptake. Prog Neurobiol 2001 · PubMed 11369436
6. US prescribing information Vigabatrin (DailyMed), section 12.1 Mechanism of Action · Prescribing information
7. Eisenberg D, Gill HS, Pfluegl GM et al. Structure-function relationships of glutamine synthetases. Biochim Biophys Acta 2000 · PubMed 10708854

Whole pathway: GABA, glutamate and glutamine

Related pathways

• Alanine — glutamate
• Citric acid cycle — succinate
• Branched-chain amino acids — Vitamin B6, Alpha-Ketoglutarat (2-Oxoglutarat)
• Carnitine — Vitamin B6, Alpha-Ketoglutarat (2-Oxoglutarat)
• Glycine and serine — Vitamin B6, Magnesium

As of 2026-09-16. Draft written by Claude to schema v2; sources checked in PubMed; expert review pending
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