Threonine
Skeletal formula
Ball-and-stick model
Names
IUPAC name
Threonine
Other names
2-Amino-3-hydroxybutanoic acid
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.000.704 Edit this at Wikidata
EC Number
  • 201-300-6
  • InChI=1S/C4H9NO3/c1-2(6)3(5)4(7)8/h2-3,6H,5H2,1H3,(H,7,8)/t2-,3+/m1/s1 checkY
    Key: AYFVYJQAPQTCCC-GBXIJSLDSA-N checkY
  • InChI=1S/C4H9NO3/c1-2(6)3(5)4(7)8/h2-3,6H,5H2,1H3,(H,7,8)/t2-,3+/m1/s1
  • Key: AYFVYJQAPQTCCC-GBXIJSLDSA-N
  • C[C@H]([C@@H](C(=O)O)N)O
Properties
C4H9NO3
Molar mass 119.120 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
Threonine (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Threonine (abbreviated as Thr or T)[2] 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 (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.

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.

History

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

Stereoisomerism

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

Threonine is one of two amino acids out of the twenty 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.

Biosynthesis

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.[3] Enzymes involved in a typical biosynthesis of threonine include:

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

Metabolism

Threonine is metabolized in two ways:

Sources

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.[4]

References

  1. ^ Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
  2. ^ "Nomenclature and symbolism for amino acids and peptides (IUPAC-IUB Recommendations 1983)", Pure Appl. Chem., 56 (5): 595–624, 1984, doi:10.1351/pac198456050595.
  3. ^ 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..
  4. ^ Carter, Herbert E.; West, Harold D. (1940). "dl-Threonine". Organic Syntheses. 20: 101; Collected Volumes, vol. 3, p. 813..