Threonine
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| Names | |
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| IUPAC name
Threonine
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| Other names
2-Amino-3-hydroxybutanoic acid
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| Identifiers | |
3D model (JSmol)
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| ChEBI | |
| ChEMBL | |
| ChemSpider | |
| DrugBank | |
| ECHA InfoCard | 100.000.704 |
| EC Number | 201-300-6 |
PubChem CID
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| UNII | |
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| Properties | |
| C4H9NO3 | |
| 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)[1] |
| Supplementary data page | |
| Refractive index (n), Dielectric constant (εr), etc. | |
Thermodynamic
data |
Phase behaviour solid–liquid–gas |
| UV, IR, NMR, MS | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). | |
 verify (what is   ?)
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| Infobox references | |
Threonine (symbol Thr or T)[2] is an amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH+
3 form under biological conditions), a carboxyl group (which is in the deprotonated −COO− form under biological conditions), and a side chain containing a hydroxyl group, making it a polar, uncharged amino acid. It is essential in humans, meaning the body cannot synthesize it: it must be obtained from the diet. Threonine is synthesized from aspartate in bacteria such as E. coli.[3] It is encoded by all the codons starting AC (ACT, ACC, ACA, and ACG).
Threonine sidechains are often hydrogen bonded; the most common small motifs formed are based on interactions with serine: ST turns, ST motifs (often at the beginning of alpha helices) and ST staples (usually at the middle of alpha helices).
Contents
Modifications[edit]
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.
It is a precursor of glycine, and can be used as a prodrug to reliably elevate brain glycine levels.
History[edit]
Threonine was the last of the 20 common proteinogenic amino acids to be discovered. It was discovered in 1936 by William Cumming Rose[4], collaborating with Curtis Meyer. The amino acid was named threonine because it was similar in structure to threonic acid, a four-carbon monosaccharide with molecular formula C4H8O5[5]
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| L-Threonine (2S,3R) and D-Threonine (2R,3S) |
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| L-Allothreonine (2S,3S) and D-Allothreonine (2R,3R) |
Threonine is one of two proteinogenic amino acids with two chiral centers, the other being isoleucine. 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-allothreonine.[6] The two stereoisomers (2R,3S)- and (2R,3R)-2-amino-3-hydroxybutanoic acid are only of minor importance.[citation needed]
Biosynthesis[edit]
As an essential amino acid, threonine is not synthesized in humans, and needs to be present in proteins in the diet. Adult humans require about 20 mg/kg body weight/day.[7] 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.[8] Enzymes involved in a typical biosynthesis of threonine include:
- aspartokinase
- β-aspartate semialdehyde dehydrogenase
- homoserine dehydrogenase
- homoserine kinase
- threonine synthase.
Metabolism[edit]
Threonine is metabolized in two ways:
- In many animals 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 the gene for threonine dehydrogenase is an inactive pseudogene[9], so threonine it is converted to α-ketobutyrate. The mechanism of the first step is analogous to that catalyzed by serine dehydratase, and the serine and threonine dehydratase reactions are probably catalyzed by the same enzyme.[10]
Sources[edit]
Foods high in threonine include cottage cheese, poultry, fish, meat, lentils, Black turtle bean[11] and Sesame seeds.[12]
Racemic threonine can be prepared from crotonic acid by alpha-functionalization using mercury(II) acetate.[13]
References[edit]
- ^ Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
- ^ "Nomenclature and Symbolism for Amino Acids and Peptides". IUPAC-IUB Joint Commission on Biochemical Nomenclature. 1983. Archived from the original on 9 October 2008. Retrieved 5 March 2018.
- ^ Raïs, Badr; Chassagnole, Christophe; Lettelier, Thierry; Fell, David; Mazat, Jean-Pierre (2001). "Threonine synthesis from aspartate in Escherichia coli cell-free extracts: pathway dynamics" (PDF). J Biochem. 356: 425–32. PMC 1221853. PMID 11368769.
- ^ A Dictionary of scientists. Daintith, John., Gjertsen, Derek. Oxford: Oxford University Press. 1999. p. 459. ISBN 9780192800862. OCLC 44963215.
- ^ Meyer, Curtis (20 July 1936). "The Spatial Configuation of Alpha-Amino-Beta-Hydroxy-n-Butyric Acid" (PDF). Journal of Biological Chemistry. 115 (3).
- ^ "Nomenclature and symbolism for amino acids and peptides (Recommendations 1983)". Pure and Applied Chemistry. 56 (5): 601, 603, 608. 1 January 1984. doi:10.1351/pac198456050595.
- ^ Institute of Medicine (2002). "Protein and Amino Acids". Dietary Reference Intakes for Energy, Carbohydrates, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press. pp. 589–768.
- ^ 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..
- ^ Stipanuk, Martha H.; Caudill, Marie A. (2013-08-13). Biochemical, Physiological, and Molecular Aspects of Human Nutrition - E-Book. Elsevier Health Sciences. ISBN 9780323266956.
- ^ Bhardwaj, Uma; Bhardwaj, Ravindra. Biochemistry for Nurses. Pearson Education India. ISBN 9788131795286.
- ^ "Error". ndb.nal.usda.gov.
- ^ "SELF Nutrition Data - Food Facts, Information & Calorie Calculator". nutritiondata.self.com. Retrieved 27 March 2018.
- ^ Carter, Herbert E.; West, Harold D. (1940). "dl-Threonine". Organic Syntheses. 20: 101.; Collective Volume, 3, p. 813.
External links[edit]
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