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Skeletal formula
Ball-and-stick model
IUPAC name
Other names
2-Amino-3-hydroxybutanoic acid
80-68-2 YesY
72-19-5 (L-isomer) N
ChEBI CHEBI:57926 YesY
ChEMBL ChEMBL291747 YesY
ChemSpider 6051 YesY
DrugBank DB00156 YesY
EC Number 201-300-6
Jmol interactive 3D Image
PubChem 6288
UNII 2ZD004190S YesY
Molar mass 119.12 g·mol−1
(H2O, g/dl) 10.6(30°),14.1(52°),19.0(61°)
Acidity (pKa) 2.63 (carboxyl), 10.43 (amino)[1]
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Phase behaviour
N verify (what is YesYN ?)
Infobox references

Threonine (abbreviated as Thr or T) is an essential, polar α-amino acid, with the formula HO2CCH(NH2)CH(OH)CH3. Together with serine, threonine is one of two proteinogenic amino acids bearing an alcohol group (tyrosine is not an alcohol but a phenol, since its hydroxyl group is bonded directly to an aromatic ring, giving it different acid/base and oxidative properties). It is also one of two common amino acids that bear a chiral side chain, along with isoleucine. Its codons are ACU, ACA, ACC, and ACG.

The threonine residue is susceptible to numerous posttranslational modifications. The hydroxyl 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.

It is a precursor of glycine, and can be used as a prodrug to reliably elevate brain glycine levels.


Threonine was discovered as the last of the 20 common proteinogenic amino acids in the 1930s by William Cumming Rose.


L-Threonin - L-Threonine.svg D-Threonine.svg
L-Threonine (2S,3R) and D-Threonine (2R,3S)
L-allo-Threonine.svg D-allo-Threonine.svg
L-allo-Threonine (2S,3S) and D-allo-Threonine (2R,3R)

Threonine is one of two proteinogenic amino acids with two chiral centers. Threonine can exist in four possible stereoisomers with the following configurations: (2S,3R), (2R,3S), (2S,3S) and (2R,3R). However, the name L-threonine is used for one single diastereomer, (2S,3R)-2-amino-3-hydroxybutanoic acid. The second stereoisomer (2S,3S), which is rarely present in nature, is called L-allo-threonine. The two stereoisomers (2R,3S)- and (2R,3R)-2-amino-3-hydroxybutanoic acid are only of minor importance.[citation needed]


As an essential amino acid, threonine is not synthesized in humans, hence we must ingest threonine in the form of threonine-containing proteins. In plants and microorganisms, threonine is synthesized from aspartic acid via α-aspartyl-semialdehyde and homoserine. Homoserine undergoes O-phosphorylation; this phosphate ester undergoes hydrolysis concomitant with relocation of the OH group.[2] Enzymes involved in a typical biosynthesis of threonine include:

  1. aspartokinase
  2. β-aspartate semialdehyde dehydrogenase
  3. homoserine dehydrogenase
  4. homoserine kinase
  5. threonine synthase.
Threonine biosynthesis


Threonine is metabolized in two ways:


Foods high in threonine include cottage cheese, poultry, fish, meat, lentils, Black turtle bean[3] and Sesame seeds.[4]

Racemic threonine can be prepared from crotonic acid by alpha-functionalization using mercury(II) acetate.[5]


  1. ^ Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
  2. ^ Lehninger, Albert L.; Nelson, David L.; Cox, Michael M. (2000), Principles of Biochemistry (3rd ed.), New York: W. H. Freeman, ISBN 1-57259-153-6 .
  3. ^
  4. ^
  5. ^ Carter, Herbert E.; West, Harold D. (1940). "dl-Threonine". Org. Synth. 20: 101. ; Coll. Vol. 3, p. 813 .

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