Threonine
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2008-07-02T12:28:34Z
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{{NatOrganicBox
| image= [[Image:Threonin - Threonine.svg|180px|Skeletal formula of threonine]]<br>[[Image:L-threonine-3D-sticks2.png|160px|3D stick model of L-threonine molecule]]
| name=(2''S'',3''R'')-2-Amino-3-hydroxybutanoic acid
| PubChem = 6288
| CAS = 72-19-5
| EINECS = 200-774-1
| SMILES = C[C@@H](O)[C@H](N)C(O)=O
| C=4 | H=9 | N=1 | O=3
| mass=119.12 g/mol
}}
'''Threonine''' (abbreviated as '''Thr''' or '''T''')<ref>{{cite web | author=IUPAC-IUBMB Joint Commission on Biochemical Nomenclature | title=Nomenclature and Symbolism for Amino Acids and Peptides | work=Recommendations on Organic & Biochemical Nomenclature, Symbols & Terminology etc | url=http://www.chem.qmul.ac.uk/iupac/AminoAcid/ | accessdate=2007-05-17}}</ref> is an α-[[amino acid]] with the [[chemical formula]] HO<sub>2</sub>CCH(NH<sub>2</sub>)CH(OH)CH<sub>3</sub>. Its [[codon]]s are ACU, ACA, ACC, and ACG. This [[essential amino acid]] is classified as [[Chemical polarity|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 modification]]s. 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.
==Allo-threonine==
With two [[Chirality (chemistry)|chiral]] centers, threonine can exist in four possible [[stereoisomer]]s, or two possible [[diastereomer]]s of <small>L</small>-threonine. However, the name <small>L</small>-threonine is used for one single [[enantiomer]], (2''S'',3''R'')-2-amino-3-hydroxybutanoic acid. The second diastereomer (2''S'',3''S''), which is rarely present in nature, is called <small>L</small>-''allo''-threonine.
==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.<ref>Nelson, D. L.; Cox, M. M. "Lehninger, Principles of Biochemistry" 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6.</ref> Enzymes involved in a typical biosynthesis of threonine include:
# [[aspartokinase]]
# α-aspartate semialdehyde [[dehydrogenase]]
# homoserine dehydrogenase
# homoserine [[kinase]]
# threonine [[synthase]].
[[Image:Thr biosynthesis.gif|thumb|center|600px|Threonine biosynthesis]]
==Metabolism==
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 [[alpha-ketobutyrate]] in a less common pathway via the enzyme [[serine dehydratase]], and thereby enters the pathway leading to [[succinyl-CoA]].
==Sources==
Foods high in threonine include [[cottage cheese]], [[poultry]], [[fish]], [[meat]], [[lentil]]s, and sesame seeds.{{Fact|date=June 2007}}
[[Racemic]] threonine can be prepared from [[crotonic acid]] by alpha-functionalization using [[mercury(II) acetate]].<ref>{{OrgSynth | author = Carter, H. E.; West, H. D. | title = dl-Threonine | collvol = 3 | collvolpages = 813 | year = 1955 | prep = cv3p0813}}</ref>
==References==
<references/>
==See also==
* [[Harold Dadford West]] American Biochemist who first synthetised the Threonine.
==External links==
*[http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/AminoAcid/Thr.html Threonine biosynthesis]
*[http://www.compchemwiki.org/index.php?title=Threonine Computational Chemistry Wiki]
*[http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=205 CID 205]
*[http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=6288 CID 6288]
{{AminoAcids}}
[[Category:Proteinogenic amino acids]]
[[Category:Glucogenic amino acids]]
[[Category:Ketogenic amino acids]]
[[Category:Essential amino acids]]
[[ca:Treonina]]
[[cs:Threonin]]
[[de:Threonin]]
[[es:Treonina]]
[[eo:Treonino]]
[[fr:Thréonine]]
[[hr:Treonin]]
[[ko:트레오닌]]
[[id:Treonin]]
[[it:Treonina]]
[[he:תראונין]]
[[lv:Treonīns]]
[[lb:Threonin]]
[[lt:Treoninas]]
[[nl:Threonine]]
[[ja:トレオニン]]
[[pl:Treonina]]
[[pt:Treonina]]
[[ru:Треонин]]
[[fi:Treoniini]]
[[sv:Treonin]]
[[tr:Treonin]]
[[uk:Треонін]]
[[zh:蘇氨酸]]