Glutamic acid
Glutamic acid, symbolized as Glu or E, is an α-amino acid that plays a crucial role in the biosynthesis of proteins across almost all living organisms[1]. It is a non-essential nutrient for humans, meaning the human body can synthesize enough for its use. Glutamic acid is the most abundant excitatory neurotransmitter in the vertebrate nervous system and serves as the precursor for the synthesis of the inhibitory gamma-aminobutyric acid (GABA) in GABAergic neurons[1].
The molecular formula of glutamic acid is C5H9NO4. It exists in two optically isomeric forms, with the dextrorotatory L-form being the one commonly obtained through various methods such as hydrolysis of gluten, from the waste waters of beet-sugar manufacture, or by fermentation[1]. The molecular structure of glutamic acid can be idealized as HOOC−CH(NH2)−(CH2)2−COOH, featuring two carboxyl groups −COOH and one amino group −NH2. However, in the solid state and mildly acidic water solutions, the molecule assumes an electrically neutral zwitterion structure −OOC−CH(NH+3)−(CH2)2−COOH[1].
Glutamic acid can lose one proton from its second carboxyl group to form the conjugate base, the singly-negative anion glutamate −OOC−CH(NH+3)−(CH2)2−COO−. This form of the compound is prevalent in neutral solutions and plays a key role in neural activation[1]. The glutamate neurotransmitter is responsible for the savory umami flavor of foods and is found in glutamate flavorings such as MSG. In Europe, it is classified as food additive E620[1].
In highly alkaline solutions, the doubly negative anion −OOC−CH(NH2)−(CH2)2−COO− prevails[1]. The radical corresponding to glutamate is called glutamyl[1].
Glutamic acid has been scientifically identified early in the 20th century for its flavor contributions, particularly the umami taste, which was first detected in seaweed[1]. It was discovered and identified in 1866 by Karl Heinrich Ritthausen, who treated wheat gluten with sulfuric acid[1]. Later, in 1908, Japanese researcher Kikunae Ikeda identified brown crystals left behind after the evaporation of a large amount of kombu broth as glutamic acid and patented a method of mass-producing a crystalline salt of glutamic acid, monosodium glutamate[1].
The relation between glutamic acid and blood pressure has been studied, with findings suggesting a stronger inverse relationship between glutamic acid intake expressed as a percentage of total protein and blood pressure compared to its expression as grams per day or percentage of kilojoules[2]. Glutamic acid is the predominant dietary amino acid, averaging 15.7 grams per day, 3.0% of kilojoules, and 20.1% of total protein in a study of 4,680 participants[2].
Commercially, L-glutamic acid is available in various forms, including powder and crystals, and is suitable for cell culture and microbiological culture[3][4]. It is also certified as a kosher product and meets certain standards for purity and quality[4].
Citations:
[1] https://en.wikipedia.org/wiki/Glutamic_acid
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4048930/
[3] https://www.sigmaaldrich.com/US/en/product/sigma/g8415
[4] https://www.sigmaaldrich.com/US/en/product/aldrich/w328502
[5] https://www.cancer.gov/publications/dictionaries/cancer-terms/def/l-glutamic-acid