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|Molar mass||117.15 g·mol−1|
|Melting point||298 °C (568 °F; 571 K) (decomposition)|
|Acidity (pKa)||2.32 (carboxyl), 9.62 (amino)|
|Supplementary data page|
|Refractive index (n),
Dielectric constant (εr), etc.
|UV, IR, NMR, MS|
|what is ?)(|
Valine (abbreviated as Val or V) encoded by the codons GUU, GUC, GUA, and GUG is an ɑ-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated -+NH3 form under biological conditions), an α-carboxylic acid group (which is in the deprotonated –COO- form under biological conditions), and a side chain isopropyl variable group, classifying it as a non-polar amino acid. It is essential in humans, meaning the body cannot synthesize it and thus it must be obtained from the diet. Human dietary sources are any proteinaceous foods such as meats, dairy products, soy products, beans and legumes.
Along with leucine and isoleucine, valine is a branched-chain amino acid. In sickle-cell disease, valine substitutes for the hydrophilic amino acid glutamic acid in β-globin. Because valine is hydrophobic, the hemoglobin is prone to abnormal aggregation.
History and etymology
Valine was first isolated from casein in 1901 by Emil Fischer. The name valine comes from valeric acid, which in turn is named after the plant valerian due to the presence of the acid in the roots of the plant.
Valine is an essential amino acid, hence it must be ingested, usually as a component of proteins. It is synthesized in plants via several steps starting from pyruvic acid. The initial part of the pathway also leads to leucine. The intermediate α-ketoisovalerate undergoes reductive amination with glutamate. Enzymes involved in this biosynthesis include:
- Acetolactate synthase (also known as acetohydroxy acid synthase)
- Acetohydroxy acid isomeroreductase
- Dihydroxyacid dehydratase
- Valine aminotransferase
- HO2CCH2CH(CH3)2 + Br2 → HO2CCHBrCH(CH3)2 + HBr
- HO2CCHBrCH(CH3)2 + 2 NH3 → HO2CCH(NH2)CH(CH3)2 + NH4Br
- Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
- Weast, Robert C., ed. (1981). CRC Handbook of Chemistry and Physics (62nd ed.). Boca Raton, FL: CRC Press. p. C-569. ISBN 0-8493-0462-8.
- "valine". Encyclopaedia Britannica Online. Retrieved 2015-12-06.
- "valine". Merriam-Webster Online Dictionary. Retrieved 2015-12-06.
- "valeric acid". Merriam-Webster Online Dictionary. Retrieved 2015-12-06.
- Jones, J. H., ed. (1985). Amino Acids, Peptides and Proteins. Specialist Periodical Reports 16. London: Royal Society of Chemistry. p. 389. ISBN 978-0-85186-144-9.
- 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.
- Marvel, C. S. (1940). "dl-Valine". Org. Synth. 20: 106.; Coll. Vol. 3, p. 848.