AskDefine | Define threonine

Dictionary Definition

threonine n : a colorless crystalline amino acid found in protein; occurs in the hydrolysates of certain proteins; an essential component of human nutrition

User Contributed Dictionary



  1. An essential amino acid C4H19NO3 found in most animal proteins.

Extensive Definition

Threonine (abbreviated as Thr or T) 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 and tyrosine, threonine is one of three 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.


With two chiral centers, threonine can exist in four possible stereoisomers, or two possible diastereomers of L-threonine. However, the name L-threonine is used for one single enantiomer, (2S,3R)-2-amino-3-hydroxybutanoic acid. The second diastereomer (2S,3S), which is rarely present in nature, is called L-allo-threonine.


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. Enzymes involved in a typical biosynthesis of threonine include:
  1. aspartokinase
  2. α-aspartate semialdehyde dehydrogenase
  3. homoserine dehydrogenase
  4. homoserine kinase
  5. threonine synthase.


Threonine is metabolized in two ways:


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.


See also

threonine in Catalan: Treonina
threonine in Czech: Threonin
threonine in German: Threonin
threonine in Spanish: Treonina
threonine in Esperanto: Treonino
threonine in French: Thréonine
threonine in Korean: 트레오닌
threonine in Indonesian: Treonin
threonine in Italian: Treonina
threonine in Hebrew: תראונין
threonine in Latvian: Treonīns
threonine in Luxembourgish: Threonin
threonine in Lithuanian: Treoninas
threonine in Dutch: Threonine
threonine in Japanese: トレオニン
threonine in Polish: Treonina
threonine in Portuguese: Treonina
threonine in Russian: Треонин
threonine in Finnish: Treoniini
threonine in Swedish: Treonin
threonine in Turkish: Treonin
threonine in Ukrainian: Треонін
threonine in Chinese: 蘇氨酸
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