Glutamine (GLN)

Glutamine is one of the 20 amino acids encoded by the standard genetic code. It is not recognized as an essential amino acid but may become conditionally essential in certain situations, including intensive athletic training or certain gastrointestinal disorders. Its side-chain is an amide formed by replacing the side-chain hydroxyl of glutamic acid with an amine functional group. Therefore, it can be considered the amide of glutamic acid. Its codons are CAA and CAG. In human blood, glutamine is the most abundant free amino acid, with a concentration of about 500-900 µmol/l. Glutamine is the most abundant naturally occurring, non-essential amino acid in the human body and one of the few amino acids that directly cross the blood-brain barrier. In the body, it is found circulating in the blood as well as stored in the skeletal muscles. It becomes conditionally essential in states of illness or injury.