Asparagine

L-Asparagine
Skeletal formula of L-asparagine
Ball-and-stick model of the L-asparagine molecule as a zwitterion
Names
IUPAC name
Asparagine
Other names
2-Amino-3-carbamoylpropanoic acid
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
DrugBank
ECHA InfoCard 100.000.669
EC Number 200-735-9
KEGG
UNII
Properties
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)
2.94 g/100 mL
Solubility soluble in acids, bases, negligible in methanol, ethanol, ether, benzene
log P −3.82
Acidity (pKa) 2.02 (carboxyl), 8.80 (amino)[1]
-69.5·10−6 cm3/mol
Structure
orthorhomic
Thermochemistry
−789.4 kJ/mol
Hazards
Safety data sheet See: data page
Sigma-Alrich
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
0
1
0
Flash point 219 °C (426 °F; 492 K)
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).
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Infobox references

Asparagine (abbreviated as Asn or N), encoded by the codons AAU and AAC,[2] 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 carboxamide, classifying it as a polar (at physiological pH), aliphatic amino acid. It is non-essential in humans, meaning the body can synthesize it. A reaction between asparagine and reducing sugars or other source of carbonyls produces acrylamide in food when heated to sufficient temperature. These products occur in baked goods such as French fries, potato chips, and toasted bread.

History

Asparagine was first isolated in 1806 in 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 chosen name. It was the first amino acid to be isolated.

Three years later, in 1809, Pierre Jean Robiquet identified a substance from liquorice root with properties he qualified as very similar to those of asparagine, and that Plisson identified in 1828 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 of alpha-helices as asx turns and asx motifs, and in similar turn motifs, or as amide rings, 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 for capping.

Asparagine also provides key sites for N-linked glycosylation, modification of the protein chain with the addition of carbohydrate chains. Typically, a carbohydrate tree can solely be added to an asparagine residue if the latter is flanked on the C side by X-serine or X-threonine, where X is any amino acid with the exception of proline.[6]

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.

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.

Degradation

Asparagine usually enters the citric acid cycle in humans as oxaloacetate. 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 (Krebs cycle). Asparagine is hydrolyzed to aspartate by asparaginase. Aspartate then undergoes transamination to form glutamate and oxaloacetate from alpha-ketoglutarate.

Function

Asparagine is required for development and function of the brain.[7] 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.[8] This glycosylation is important both for protein structure[9] and protein function.[10]

Betaine structure

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

References

  1. ↑ R. M. C. Dawson; Daphne Elliott; W. H. Elliott; K. M. Jones. Clarendon, eds. (1959). Data for Biochemical Research. Oxford: Clarendon Press. OCLC 644267041.
  2. ↑ "Nomenclature and symbolism for amino acids and peptides (IUPAC-IUB Recommendations 1983)", Pure Appl. Chem., 56 (5): 595–624, 1984, doi:10.1351/pac198456050595
  3. ↑ Vauquelin LN, Robiquet PJ (1806). "La découverte d'un nouveau principe végétal dans le suc des asperges". Annales de Chimie (in French). 57: 88–93.
  4. ↑ R.H.A. Plimmer (1912) [1908]. R.H.A. Plimmer; F.G. Hopkins, eds. 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. ↑ Harvey Wickes Felter, M.D. & John Uri Lloyd (1898). "Glycyrrhiza (U. S. P.)—Glycyrrhiza". King's American Dispensatory. Henriette's Herbal Homepage.
  6. ↑ Brooker, Robert; Widmaier, Eric; Graham, Linda; Stiling, Peter; Hasenkampf, Clare; Hunter, Fiona; Bidochka, Michael; Riggs, Daniel (2010). "Chapter 5: Systems Biology of Cell Organization". Biology (Canadian ed.). United States of America: McGraw-Hill Ryerson. pp. 105–106. ISBN 978-0-07-074175-1.
  7. ↑ Ruzzo, EK; et, al (2013). "Deficiency of asparagine synthetase causes congenital microcephaly and a progressive form of encephalopathy". Neuron. 80 (2): 429–41. PMC 3820368 Freely accessible. PMID 24139043. doi:10.1016/j.neuron.2013.08.013.
  8. ↑ Burda, Patricie; Aebi, Markus (1999). "The dolichol pathway of N-linked glycosylation". Biochimica et Biophysica Acta (BBA) - General Subjects. 1426 (2): 239–257. doi:10.1016/S0304-4165(98)00127-5.
  9. ↑ Imperiali, Barbara; o’Connor, Sarah E (1999). "Effect of N-linked glycosylation on glycopeptide and glycoprotein structure". Current Opinion in Chemical Biology. 3 (6): 643–9. PMID 10600722. doi:10.1016/S1367-5931(99)00021-6.
  10. ↑ Patterson, Marc C. (2005). "Metabolic Mimics: The Disorders of N-Linked Glycosylation". Seminars in Pediatric Neurology. 12 (3): 144–51. PMID 16584073. doi:10.1016/j.spen.2005.10.002.
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