|Jmol interactive 3D||Image|
|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)|
|Supplementary data page|
|Refractive index (n),
Dielectric constant (εr), etc.
|UV, IR, NMR, MS|
|what is ?)(|
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.
|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 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.
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:
- β-aspartate semialdehyde dehydrogenase
- homoserine dehydrogenase
- homoserine kinase
- threonine synthase.
Threonine is metabolized in two ways:
- It is converted to pyruvate via threonine dehydrogenase. An intermediate in this pathway can undergo thiolysis with CoA to produce acetyl-CoA and glycine.
- In humans, it is converted to α-ketobutyrate in a less common pathway via the enzyme serine dehydratase, and thereby enters the pathway leading to succinyl-CoA.
- Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
- 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.
- Carter, Herbert E.; West, Harold D. (1940). "dl-Threonine". Org. Synth. 20: 101.; Coll. Vol. 3, p. 813.