Glutamic acid (or glutamate) functions as a neurotransmitter and also serves as a precursor to other neurotransmitters such as gamma-aminobutyric acid. Glutamic acid also plays a key role in many metabolic pathways that controls growth, reproduction, maintenance and immunity. It is converted to α-ketoglutarate, a key component of the TCA (tricarboxylic acid) cycle and a precursor for the biosynthesis of nucleic acids and certain amino acids. In cells, glutamine is converted to glutamate by the enzyme glutaminase. Appl- L-Glutamic acid-2,3,3,4,4-d5 has been used as an internal standard in metabolomics and lipidomics profiling.