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Alanine (abbreviated as Ala or A) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated form, −NH3+, under biological conditions), an α-carboxylic acid group (which is in the deprotonated form, −COO, under biological conditions), and a side chain methyl group, making it a nonpolar, aliphatic amino acid. It is non-essential in humans: because the body can synthesize it, it does not need to be present in the diet. It is one of the 20 amino acids encoded by the human genetic code, and is encoded by all codons starting with GC, namely GCU, GCC, GCA, and GCG.

Alanine
Alanine at physiological pH
Alanine in non-ionic form
Names
IUPAC name
Alanine
Other names
2-Aminopropanoic acid
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.000.249
EC Number 206-126-4
KEGG
UNII
Properties
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]
-50.5·10−6 cm3/mol
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

The L-isomer of alanine (left-handed) is the one that is incorporated into proteins. 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.[2] The right-handed form, D-Alanine occurs in polypeptides in some bacterial cell walls[3]p.131 and in some peptide antibiotics, and occurs in the tissues of many crustaceans and molluscs as an osmolyte.[4]

Contents

History and etymologyEdit

Alanine was first synthesized in 1850 by Adolph Strecker.[5][6][7] The amino acid was named Alanin in German, in reference to aldehyde, with the infix -an- for ease of pronunciation,[8] the German ending -in used in chemical compounds being analogous to English -ine.

StructureEdit

Alanine is an aliphatic amino acid, because the side-chain connected to the α-carbon atom is a methyl group (-CH3), making it the simplest α-amino acid except for glycine. The methyl side-chain of alanine is non-reactive and is therefore hardly ever directly involved in protein function.[9]

Because alanine's side-chain cannot be phosphorylated, it is useful in loss of function experiments with respect to phosphorylation. Some techniques involve creating a library of genes, each of which has a point mutation at a different position in the area of interest, sometimes even every position in the whole gene: this is called "scanning mutagenesis". The simplest method, and the first to have been used, is so-called "alanine scanning", where every position in turn is mutated to alanine.[10]

SourcesEdit

Dietary sourcesEdit

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

BiosynthesisEdit

Alanine can be synthesized from pyruvate and branched chain amino acids such as valine, leucine, and isoleucine.

Alanine is most commonly produced by reductive amination of pyruvate, a two-step process. In the first step, α-ketoglutarate, ammonia and NADH are converted by glutamate dehydrogenase to glutamate, NAD+ and water. In the second step, the amino group of the newly-formed glutamate is transferred to pyruvate by an aminotransferase enzyme, regenerating the α-ketoglutarate, and converting the pyruvate to alanine. The net result is that pyruvate and ammonia are converted to alanine, consuming one reducing equivalent.[3]p.721 Because transamination reactions are readily reversible and pyruvate is present in all cells, alanine can be easily formed and thus has close links to metabolic pathways such as glycolysis, gluconeogenesis, and the citric acid cycle.

Chemical synthesisEdit

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:[11]

 
 
 
L-Alanine Synthesis.[12]

DegradationEdit

Alanine is broken down by oxidative deamination, the inverse reaction of the reductive amination reaction described above, catalyzed by the same enzymes. The direction of the process is largely controlled by the relative concentration of the substrates and products of the reactions involved.[3]p.721

Physiological functionEdit

Glucose–alanine cycleEdit

In mammals, 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 to pyruvate, a product of muscle glycolysis, through the action of alanine aminotransferase, forming alanine and α-ketoglutarate. The alanine enters the bloodstream, and is transported to the liver. The alanine aminotransferase reaction takes place in reverse in the liver, where the regenerated pyruvate is used in gluconeogenesis, forming glucose which returns to the muscles through the circulation system. Glutamate in the liver enters mitochondria and is broken down by glutamate dehydrogenase into α-ketoglutarate and ammonium, which in turn participates in the urea cycle to form urea which is excreted through the kidneys.[13]

The glucose–alanine cycle enables pyruvate and glutamate to be removed from the muscle and safely transported to the liver, where glucose is regenerated from pyruvate and then returned to muscle: this moves the energetic burden of gluconeogenesis to the liver instead of the muscle, and all available ATP in the muscle can be devoted to muscle contraction.[13] It is a catabolic pathway, and relies upon protein breakdown in the muscle tissue. Whether and to what extent it occurs in non-mammals is unclear.[14][15]

Link to diabetesEdit

Alterations in the alanine cycle that increase the levels of serum alanine aminotransferase (ALT) are linked to the development of type II diabetes.[16]

Chemical propertiesEdit

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

Free radical stabilityEdit

The deamination of an alanine molecule produces a stable alkyl free radical, CH3CHCOO. Deamination can be induced in solid or aqueous alanine by radiation.[17]

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.[18] This is considered to be a biologically relevant measure of the amount of radiation damage that living tissue would suffer under the same radiation exposure.[18] 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.

ReferencesEdit

  1. ^ Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
  2. ^ 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 .
  3. ^ a b c Mathews, Christopher K., (2000). Biochemistry. Van Holde, K. E., Ahern, Kevin G. (3rd ed ed.). San Francisco, Calif.: Benjamin Cummings. ISBN 0805330666. OCLC 42290721. 
  4. ^ Yoshimura, Tohru; Nishikawa, Toru; Homma, Hiroshi (2016-08-25). D-Amino Acids: Physiology, Metabolism, and Application. Springer. ISBN 9784431560777. 
  5. ^ Strecker, A. (1850). "Ueber die künstliche Bildung der Milchsäure und einen neuen, dem Glycocoll homologen" [On the artificial formation of lactic acid and a new substance homologous to glycine]. Annalen der Chemie und Pharmacie. 75 (1): 27–45. doi:10.1002/jlac.18500750103.  Strecker names alanine on p. 30.
  6. ^ Strecker, A. (1854). "Ueber einen neuen aus Aldehyd – Ammoniak und Blausäure entstehenden Körper" [On a new substance arising from acetaldehyde–ammonia [i.e., 1-aminoethanol] and hydrocyanic acid]. Annalen der Chemie und Pharmacie. 91 (3): 349–351. doi:10.1002/jlac.18540910309. 
  7. ^ "Alanine". 
  8. ^ "alanine". Oxford Dictionaries. Retrieved 2015-12-06. 
  9. ^ Textbook of Biotechnology. McGraw-Hill Education (I). 2012. ISBN 9780071070072. 
  10. ^ Park, Sheldon J.; Cochran, Jennifer R. (2009-09-25). Protein Engineering and Design. CRC Press. ISBN 9781420076592. 
  11. ^ Kendall, E. C.; McKenzie, B. F. (1929). "dl-Alanine". Org. Synth. 9: 4. ; Coll. Vol., 1, p. 21 .
  12. ^ http://drugsynthesis.blogspot.co.uk/2011/11/laboratory-synthesis-of-l-alanine.html
  13. ^ a b 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 .
  14. ^ Fish Physiology: Nitrogen Excretion. Academic Press. 2001-09-07. p. 23. ISBN 9780080497518. 
  15. ^ Walsh, Patrick J.; Wright, Patricia A. (1995-08-31). Nitrogen Metabolism and Excretion. CRC Press. ISBN 9780849384110. 
  16. ^ "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". 
  17. ^ 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 .
  18. ^ a b Pedro,, Andreo, (2017). Fundamentals of ionizing radiation dosimetry. Burns, David T.,, Nahum, Alan E.,, Seuntjens, Jan P.,, Attix, Frank H., (2nd edition ed.). Weinheim, Germany: WILEY-VCH. p. 547. ISBN 9783527808236. OCLC 990023546. 

External linksEdit