Threonine 63553 223067745 2008-07-02T12:28:34Z Vedran12 7322109 interwiki hr {{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]]