Glutamine (abbreviated as Gln or Q, and often called L-glutamine) is one of the 20 amino acids encoded by the standard genetic code. It is considered a conditionally essential amino acid. Its side-chain is an amide formed by replacing the side-chain hydroxyl of glutamic acid with an amine functional group, making it 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.