Alanine

Alanine
Names
IUPAC name
Alanine
Other names
2-Aminopropanoic acid
Identifiers
338-69-2 (D-isomer) Yes
56-41-7 (L-isomer) Yes
302-72-7 (racemic) Yes
ChEBI CHEBI:16977 
ChEMBL ChEMBL66693 Yes
ChemSpider 64234 (D-isomer) Yes
5735 (L-isomer) Yes
582 (Racemic) Yes
EC-number 206-126-4
IUPHAR ligand 720
Jmol-3D images Image
Image
KEGG C01401 
PubChem 5950
UNII 1FU7983T0U 
Properties
Molecular formula
 C3H7NO2
Molar mass 89.09 g·mol−1
Appearance white powder
Density 1.424 g/cm3
Melting point 258 °C (496 °F; 531 K) (sublimes)
167.2 g/L (25 °C)
Acidity (pKa) 2.35 (carboxyl), 9.69 (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 noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Alanine (abbreviated as Ala or A)[2] is an α-amino acid with the chemical formula CH3CH(NH2)COOH. The L-isomer is one of the 20 amino acids encoded by the genetic code. Its codons are GCU, GCC, GCA, and GCG. It is classified as a non-polar amino acid. L-Alanine is second only to leucine in rate of occurrence, accounting for 7.8% of the primary structure in a sample of 1,150 proteins.[3] D-Alanine occurs in bacterial cell walls and in some peptide antibiotics.

Structure

The α-carbon atom of alanine is bound with a methyl group (-CH3), making it one of the simplest α-amino acids with respect to molecular structure and also resulting in alanine's being classified as an aliphatic amino acid. The methyl group of alanine is non-reactive and is thus almost never directly involved in protein function.

Sources

Dietary sources

Alanine is a nonessential amino acid, meaning it can be manufactured by the human body, and does not need to be obtained directly through the diet. Alanine is found in a wide variety of foods, but is particularly concentrated in meats.

Good sources of alanine include

Biosynthesis

Alanine can be manufactured in the body from pyruvate and branched chain amino acids such as valine, leucine, and isoleucine.

Alanine is most commonly produced by reductive amination of pyruvate. Because transamination reactions are readily reversible and pyruvate pervasive, alanine can be easily formed and thus has close links to metabolic pathways such as glycolysis, gluconeogenesis, and the citric acid cycle. It also arises together with lactate and generates glucose from protein via the alanine cycle.

Chemical synthesis

Racemic alanine can be prepared by the condensation of acetaldehyde with ammonium chloride in the presence of sodium cyanide by the Strecker reaction, or by the ammonolysis of 2-bromopropanoic acid:[4]

L-Alanine Synthesis.[5]

Physiological function

Glucose–alanine cycle

Alanine plays a key role in glucose–alanine cycle between tissues and liver. In muscle and other tissues that degrade amino acids for fuel, amino groups are collected in the form of glutamate by transamination. Glutamate can then transfer its amino group through the action of alanine aminotransferase to pyruvate, a product of muscle glycolysis, forming alanine and α-ketoglutarate. The alanine formed is passed into the blood and transported to the liver. A reverse of the alanine aminotransferase reaction takes place in liver. Pyruvate regenerated forms glucose through gluconeogenesis, which returns to muscle through the circulation system. Glutamate in the liver enters mitochondria and degrades into ammonium ion through the action of glutamate dehydrogenase, which in turn participate in the urea cycle to form urea.[6]

The glucose–alanine cycle enables pyruvate and glutamate to be removed from the muscle and find their way to the liver. Glucose is regenerated from pyruvate and then returned to muscle: the energetic burden of gluconeogenesis is thus imposed on the liver instead of the muscle. All available ATP in muscle is devoted to muscle contraction.[6]

Link to hypertension

An international study led by Imperial College London found a correlation between high levels of alanine and higher blood pressure, energy intake, cholesterol levels, and body mass index.[7]

(S)-Alanine (left) and (R)-alanine (right) in zwitterionic form at neutral pH

Link to diabetes

Alterations in the alanine cycle that increase the levels of serum alanine aminotransferase (ALT) is linked to the development of type II diabetes. With an elevated level of ALT the risk of developing type II diabetes increases.[8]

Chemical properties

Free radical stability

The deamination of an alanine molecule produces a stable alkyl free radical, CH3C•HCOO−. Deamination can be induced in solid or aqueous alanine by radiation.[9]

This property of alanine is used in dosimetric measurements in radiotherapy. When normal alanine is irradiated, the radiation causes certain alanine molecules to become free radicals, and, as these radicals are stable, the free radical content can later be measured by electron paramagnetic resonance in order to find out how much radiation the alanine was exposed to. Radiotherapy treatment plans can be delivered in test mode to alanine pellets, which can then be measured to check that the intended pattern of radiation dose is correctly delivered by the treatment system.

See also

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, doi:10.1351/pac198456050595.
  3. ↑ Doolittle, R. F. (1989), "Redundancies in protein sequences", in Fasman, G. D., Prediction of Protein Structures and the Principles of Protein Conformation, New York: Plenum, pp. 599–623, ISBN 0-306-43131-9.
  4. ↑ Kendall, E. C.; McKenzie, B. F. (1929). "dl-Alanine". Org. Synth. 9: 4.; Coll. Vol. 1, p. 21.
  5. ↑ http://drugsynthesis.blogspot.co.uk/2011/11/laboratory-synthesis-of-l-alanine.html
  6. ↑ 6.0 6.1 Nelson, David L.; Cox, Michael M. (2005), Principles of Biochemistry (4th ed.), New York: W. H. Freeman, pp. 684–85, ISBN 0-7167-4339-6.
  7. ↑ Highfield, Roger (2008-04-21), "'Metabolic fingerprint' linked to high blood pressure", Daily Telegraph.
  8. ↑ "Elevated Alanine Aminotransferase Predicts New-Onset Type 2 Diabetes Independently of Classical Risk Factors, Metabolic Syndrome, and C-Reactive Protein in the West of Scotland Coronary Prevention Study".
  9. ↑ Zagórski, Z. P.; Sehested, K. (1998), "Transients and stable radical from the deamination of α-alanine", J. Radioanal. Nucl. Chem. 232 (1–2): 139–41, doi:10.1007/BF02383729.

External links