Threonine

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Threonine


IUPAC name Threonine
Other names 2-Amino-3-hydroxybutanoic acid
Identifiers
CAS number	80-68-2^Y, 72-19-5 (L-isomer)
PubChem	6288
ChemSpider	6051^Y
EC number	201-300-6
DrugBank	DB00156
ChEBI	CHEBI:57926^Y
ChEMBL	CHEMBL291747^Y
Jmol-3D images	{{#if:C[C@H]([C@@H](C(=O)O)N)O\|Image 1
SMILES C[C@H]([C@@H](C(=O)O)N)O
InChI InChI=1S/C4H9NO3/c1-2(6)3(5)4(7)8/h2-3,6H,5H2,1H3,(H,7,8)/t2-,3+/m1/s1^Y Key: AYFVYJQAPQTCCC-GBXIJSLDSA-N^Y InChI=1S/C4H9NO3/c1-2(6)3(5)4(7)8/h2-3,6H,5H2,1H3,(H,7,8)/t2-,3+/m1/s1
Properties
Molecular formula	C₄H₉NO₃
Molar mass	119.12 g mol⁻¹
Solubility in water	(H2O, g/dl) 10.6(30°),14.1(52°),19.0(61°)
Acidity (pK_a)	2.63 (carboxyl), 10.43 (amino)^[1]
Supplementary data page
Structure and properties	n, ε_r, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Threonine (abbreviated as Thr or T)^[2] is an α-amino acid with the chemical formula HO₂CCH(NH₂)CH(OH)CH₃. Its codons are ACU, ACA, ACC, and ACG. This essential amino acid is classified as polar. 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.

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.

History

Threonine was discovered as the last of the 20 common proteinogenic amino acids in the 1930s by William Cumming Rose.

Stereoisomerism


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. ^{[citation needed]}

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.^[3] Enzymes involved in a typical biosynthesis of threonine include:

aspartokinase
β-aspartate semialdehyde dehydrogenase
homoserine dehydrogenase
homoserine kinase
threonine synthase.

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 α-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, lentils, Black turtle bean^[4] and Sesame seeds.^[5]

Racemic threonine can be prepared from crotonic acid by alpha-functionalization using mercury(II) acetate.^[6]

References

↑ Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
↑ "Nomenclature and symbolism for amino acids and peptides (IUPAC-IUB Recommendations 1983)", Pure Appl. Chem. 56 (5), 1984: 595–624, doi:10.1351/pac198456050595 .
↑ 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 .
↑ http://ndb.nal.usda.gov/ndb/foods/show/4632?fg=&man=&lfacet=&count=&max=&sort=&qlookup=&offset=&format=Full&new=
↑ http://nutritiondata.self.com/
↑ Carter, Herbert E.; West, Harold D. (1940), "dl-Threonine", Org. Synth. 20: 101 ; Coll. Vol. 3: 813 .

External links

The 20 common amino acids

General topics

By properties

Aliphatic	Branched-chain amino acids (Valine Isoleucine Leucine) Methionine Alanine Proline Glycine

Aromatic	Phenylalanine Tyrosine Tryptophan Histidine

Polar, uncharged	Asparagine Glutamine Serine Threonine

Positive charge (pK_a)	Lysine (≈10.8) Arginine (≈12.5) Histidine (≈6.1)

Negative charge (pK_a)	Aspartic acid (≈3.9) Glutamic acid (≈4.1) Cysteine (≈8.3) Tyrosine (≈10.1)

Other classifications

Biochemical families: carbohydrates
- alcohols
- glycoproteins
- glycosides
lipids
- eicosanoids
- fatty acids / intermediates
- phospholipids
- sphingolipids
- steroids
nucleic acids
- constituents / intermediates
proteins
- Amino acids / intermediates
tetrapyrroles / intermediates

Amino acid metabolism metabolic intermediates

K→acetyl-CoA

lysine→	Saccharopine Allysine α-Aminoadipic acid α-Aminoadipate Glutaryl-CoA Glutaconyl-CoA Crotonyl-CoA β-Hydroxybutyryl-CoA

leucine→	α-Ketoisocaproic acid Isovaleryl-CoA 3-Methylcrotonyl-CoA 3-Methylglutaconyl-CoA HMG-CoA

tryptophan→alanine→	N'-Formylkynurenine Kynurenine Anthranilic acid 3-Hydroxykynurenine 3-Hydroxyanthranilic acid 2-Amino-3-carboxymuconic semialdehyde 2-Aminomuconic semialdehyde 2-Aminomuconic acid Glutaryl-CoA

G→pyruvate→citrate

glycine→serine→	3-Phosphoglyceric acid glycine→creatine: Glycocyamine Phosphocreatine Creatinine

G→glutamate→
α-ketoglutarate

histidine→	Urocanic acid Imidazol-4-one-5-propionic acid Formiminoglutamic acid Glutamate-1-semialdehyde

proline→	1-Pyrroline-5-carboxylic acid

arginine→	Ornithine Putrescine Agmatine

other	cysteine+glutamate→glutathione: γ-Glutamylcysteine

G→propionyl-CoA→
succinyl-CoA

valine→	α-Ketoisovaleric acid Isobutyryl-CoA Methacrylyl-CoA 3-Hydroxyisobutyryl-CoA 3-Hydroxyisobutyric acid 2-Methyl-3-oxopropanoic acid

isoleucine→	2,3-Dihydroxy-3-methylpentanoic acid 2-Methylbutyryl-CoA Tiglyl-CoA 2-Methylacetoacetyl-CoA

methionine→	generation of homocysteine: S-Adenosyl methionine S-Adenosyl-L-homocysteine Homocysteine conversion to cysteine: Cystathionine alpha-Ketobutyric acid+Cysteine

threonine→	α-Ketobutyric acid

propionyl-CoA→	Methylmalonyl-CoA

G→fumarate

phenylalanine→tyrosine→	4-Hydroxyphenylpyruvic acid Homogentisic acid 4-Maleylacetoacetate

G→oxaloacetate

see urea cycle

Other

Cysteine metabolism	Cysteine sulfinic acid

M: MET

mt, k, c/g/r/p/y/i, f/h/s/l/o/e, a/u, n, m

k, cgrp/y/i, f/h/s/l/o/e, au, n, m, epon

m (A16/C10), i (k, c/g/r/p/y/i, f/h/s/o/e, a/u, n, m)

Biochemical families: carbohydrates
- alcohols
- glycoproteins
- glycosides
lipids
- eicosanoids
- fatty acids / intermediates
- phospholipids
- sphingolipids
- steroids
nucleic acids
- constituents / intermediates
proteins
- Amino acids / intermediates
tetrapyrroles / intermediates

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