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Threonine (abbreviated as Thr or T) is an α-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), an α-carboxylic acid 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.[2] In the genetic code it is encoded by the codons ACU, ACC, ACA, and ACG.

Threonine
Skeletal formula
Ball-and-stick model
Names
IUPAC name
Threonine
Other names
2-Amino-3-hydroxybutanoic acid
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
DrugBank
ECHA InfoCard 100.000.704
EC Number 201-300-6
UNII
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 constantr), 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).
N verify (what is YesYN ?)
Infobox references

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

ModificationsEdit

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.

HistoryEdit

Threonine was the last of the 20 common proteinogenic amino acids to be discovered. It was discovered in 1936 by William Cumming Rose[3], collaborating with Curtis Meyer. The amino acid was named threonine because it was similar in structure to threose, a four-carbon monosaccharide with molecular formula C4H8O4[4]

   
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, 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-allo-threonine. The two stereoisomers (2R,3S)- and (2R,3R)-2-amino-3-hydroxybutanoic acid are only of minor importance.[citation needed]

BiosynthesisEdit

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.[5] 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.[6] Enzymes involved in a typical biosynthesis of threonine include:

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

MetabolismEdit

Threonine is metabolized in two ways:

SourcesEdit

Foods high in threonine include cottage cheese, poultry, fish, meat, lentils, Black turtle bean[9] and Sesame seeds.[10]

Racemic threonine can be prepared from crotonic acid by alpha-functionalization using mercury(II) acetate.[11]

ReferencesEdit

  1. ^ Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
  2. ^ 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. 
  3. ^ A Dictionary of scientists. Daintith, John., Gjertsen, Derek. Oxford: Oxford University Press. 1999. p. 459. ISBN 9780192800862. OCLC 44963215. 
  4. ^ Meyer, Curtis (20 July 1936). "The Spatial Configuation of Alpha-Amino-Beta-Hydroxy-n-Butyric Acid" (PDF). Journal of Biological Chemistry. 115 (3). 
  5. ^ 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. 
  6. ^ 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. .
  7. ^ Stipanuk, Martha H.; Caudill, Marie A. (2013-08-13). Biochemical, Physiological, and Molecular Aspects of Human Nutrition - E-Book. Elsevier Health Sciences. ISBN 9780323266956. 
  8. ^ Bhardwaj, Uma; Bhardwaj, Ravindra. Biochemistry for Nurses. Pearson Education India. ISBN 9788131795286. 
  9. ^ http://ndb.nal.usda.gov/ndb/foods/show/4632?fg=&man=&lfacet=&count=&max=&sort=&qlookup=&offset=&format=Full&new=
  10. ^ http://nutritiondata.self.com/
  11. ^ Carter, Herbert E.; West, Harold D. (1940). "dl-Threonine". Org. Synth. 20: 101. ; Coll. Vol., 3, p. 813 .

External linksEdit