Threonine (Thr)

Threonine is an α-amino acid with the chemical formula HO₂CCH(NH₂)CH(OH)CH₃. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar. Together with serine, threonine is one of two proteinogenic amino acids bearing an alcohol group.

The threonine residue is susceptible to numerous posttranslational modifications. The hydroxy side chain can undergo O-linked glycosylation. In addition, threonine residues undergo phosphorylation through the action of a threonine kinase. In its phosphorylated form, it can be referred to as phosphothreonine. Foods high in threonine include cottage cheese, poultry, fish, meat, lentils, and sesame seeds.Racemic threonine can be prepared from crotonic acid by alpha-functionalization using mercury(II) acetate.