Glutamate

Glutamic acid (abbreviated as Glu or E) is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid. The carboxylate anions and salts of glutamic acid are known as glutamates. In neuroscience, glutamate is an important neurotransmitter that plays a key role in long-term potentiation and is important for learning and memory.

Biosynthesis

Reactants	Products	Enzymes
Glutamine + H2O	→ Glu + NH3	GLS, GLS2
NAcGlu + H2O	→ Glu + Acetate	(unknown)
α-ketoglutarate + NADPH + NH4+	→ Glu + NADP+ + H2O	GLUD1, GLUD2
α-ketoglutarate + α-amino acid	→ Glu + α-oxo acid	transaminase
1-Pyrroline-5-carboxylate + NAD+ + H2O	→ Glu + NADH	ALDH4A1
N-formimino-L-glutamate + FH4	→ Glu + 5-formimino-FH4	FTCD

Function and uses

Metabolism

Glutamate is a key molecule in cellular metabolism. In humans, dietary proteins are broken down by digestion into amino acids, which serve as metabolic fuel for other functional roles in the body. A key process in amino acid degradation is transamination, in which the amino group of an amino acid is transferred to an α-ketoacid, typically catalysed by a transaminase. The reaction can be generalised as such:

R₁-amino acid + R₂-α-ketoacid ⇌ R₁-α-ketoacid + R₂-amino acid

A very common α-keto acid is α-ketoglutarate, an intermediate in the citric acid cycle. Transamination of α-ketoglutarate gives glutamate. The resulting α-ketoacid product is often a useful one as well, which can contribute as fuel or as a substrate for further metabolism processes. Examples are as follows:

Alanine + α-ketoglutarate ⇌ pyruvate + glutamate

Aspartate + α-ketoglutarate ⇌ oxaloacetate + glutamate

Both pyruvate and oxaloacetate are key components of cellular metabolism, contributing as substrates or intermediates in fundamental processes such as glycolysis, gluconeogenesis, and the citric acid cycle.
Glutamate also plays an important role in the body's disposal of excess or waste nitrogen. Glutamate undergoes deamination, an oxidative reaction catalysed by glutamate dehydrogenase, as follows:

glutamate + H₂O + NADP⁺ → α-ketoglutarate + NADPH + NH₃ + H⁺

Ammonia (as ammonium) is then excreted predominantly as urea, synthesised in the liver. Transamination can, thus, be linked to deamination, effectively allowing nitrogen from the amine groups of amino acids to be removed, via glutamate as an intermediate, and finally excreted from the body in the form of urea.