Asparagine

Asparagine

L-Asparagine
Skeletal formula of L-isomer
Ball-and-stick model of L-isomer
Identifiers
CAS number  YesY
PubChem
ChemSpider  YesY
UNII  YesY
EC-number
DrugBank
KEGG  YesY
ChEBI  YesY
ChEMBL  YesY
Jmol-3D images Image 1
Image 2
Properties
Molecular formula C4H8N2O3
Molar mass 132.12 g mol−1
Appearance white crystals
Density 1.543 g/cm3
Melting point 234 °C (453 °F; 507 K)
Boiling point 438 °C (820 °F; 711 K)
Solubility in water 2.94 g/100 mL
Solubility soluble in acid, alkali
negligible in methanol, ethanol, ether, benzene
log P -3.82
Acidity (pKa) 2.02 (carboxyl), 8.80 (amino)[1]
Structure
Crystal structure orthorhomic
Thermochemistry
Std enthalpy of
formation
ΔfHo298
-789.4 kJ/mol
Hazards
MSDS External MSDS
NFPA 704
0
1
0
Flash point 219 °C (426 °F; 492 K)
Supplementary data page
Structure and
properties
n, εr, etc.
Thermodynamic
data
Phase behaviour
Solid, liquid, gas
Spectral data UV, IR, NMR, MS
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY   YesY/N?)

Asparagine (abbreviated as Asn or N) is one of the 20 most common natural amino acids on Earth. It has carboxamide as the side-chain's functional group. It is not an essential amino acid. Its codons are AAU and AAC.[2]

A reaction between asparagine and reducing sugars or reactive carbonyls produces acrylamide (acrylic amide) in food when heated to sufficient temperature. These products occur in baked goods such as French fries, potato chips, and toasted bread.

Contents

  • History 1
  • Structural function in proteins 2
  • Sources 3
    • Dietary sources 3.1
    • Biosynthesis 3.2
  • Degradation 4
  • Function 5
  • Betaine structure 6
  • External links 7
  • References 8

History

Asparagine was first isolated in 1806, under a crystalline form, by French chemists Louis Nicolas Vauquelin and Pierre Jean Robiquet (then a young assistant) from asparagus juice,[3][4] in which it is abundant — hence, the name they chose for that new matter — becoming the first amino acid to be isolated.

A few years later, in 1809, Pierre Jean Robiquet again identified, this time from liquorice root, a substance with properties he qualified as very similar to those of asparagine, that Plisson in 1828 identified as asparagine itself.[5]

Structural function in proteins

Since the asparagine side-chain can form hydrogen bond interactions with the peptide backbone, asparagine residues are often found near the beginning and the end of alpha-helices, and in turn motifs in beta sheets. Its role can be thought as "capping" the hydrogen bond interactions that would otherwise be satisfied by the polypeptide backbone. Glutamines, with an extra methylene group, have more conformational entropy and thus are less useful in this regard.

Asparagine also provides key sites for N-linked glycosylation, modification of the protein chain with the addition of carbohydrate chains.

Sources

Dietary sources

Asparagine is not essential for humans, which means that it can be synthesized from central metabolic pathway intermediates and is not required in the diet.

Asparagus is a source of L-asparagine.

Asparagine is found in:

Biosynthesis

The precursor to asparagine is oxaloacetate. Oxaloacetate is converted to aspartate using a transaminase enzyme. The enzyme transfers the amino group from glutamate to oxaloacetate producing α-ketoglutarate and aspartate. The enzyme asparagine synthetase produces asparagine, AMP, glutamate, and pyrophosphate from aspartate, glutamine, and ATP. In the asparagine synthetase reaction, ATP is used to activate aspartate, forming β-aspartyl-AMP. Glutamine donates an ammonium group, which reacts with β-aspartyl-AMP to form asparagine and free AMP.

The biosynthesis of asparagine from oxaloacetate

Degradation

Asparagine usually enters the citric acid cycle in humans as malate. In bacteria, the degradation of asparagine leads to the production of oxaloacetate which is the molecule which combines with citrate in the citric acid cycle (Kreb's cycle). Asparagine is hydrolyzed to aspartate by asparaginase. Aspartate then undergoes transamination to form glutamate and oxaloacetate from alpha-ketogluterate.

Function

The nervous system requires asparagine. It also plays an important role in the synthesis of ammonia.

The addition of N-acetylglucosamine to asparagine is performed by oligosaccharyltransferase enzymes in the endoplasmic reticulum.[6] This glycosylation is important both for protein structure[7] and protein function.[8]

Betaine structure

(S)-Asparagine (left) and (R)-asparagine (right) in zwitterionic form at neutral pH.

External links

  • GMD MS Spectrum
  • Why Asparagus Makes Your Pee Stink


References

  1. ^ Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
  2. ^ "Nomenclature and symbolism for amino acids and peptides (IUPAC-IUB Recommendations 1983)", Pure Appl. Chem. 56 (5), 1984: 595–624,  .
  3. ^ Vauquelin LN, Robiquet PJ (1806). "La découverte d'un nouveau principe végétal dans le suc des asperges". Annales de Chimie 57: 88–93. 
  4. ^ R.H.A. Plimmer (1912) [1908]. R.H.A. Plimmer & F.G. Hopkins, ed. The chemical composition of the proteins. Monographs on biochemistry. Part I. Analysis (2nd ed.). London: Longmans, Green and Co. p. 112. Retrieved January 18, 2010. 
  5. ^ http://www.henriettesherbal.com/eclectic/kings/glycyrrhiza.html
  6. ^ Burda P, Aebi M (January 1999). "The dolichol pathway of N-linked glycosylation". Biochim. Biophys. Acta 1426 (2): 239–57. doi:10.1016/S0304-4165(98)00127-5
  7. ^ Imperiali B, O'Connor SE (December 1999). "Effect of N-linked glycosylation on glycopeptide and glycoprotein structure". Curr Opin Chem Biol 3 (6): 643–9. doi:10.1016/S1367-5931(99)00021-6. PMID 10600722
  8. ^ Patterson MC (September 2005). "Metabolic mimics: the disorders of N-linked glycosylation". Semin Pediatr Neurol 12 (3): 144–51. doi:10.1016/j.spen.2005.10.002