Valine

Valine
Names
IUPAC name
Valine
Other names
2-amino-3-methylbutanoic acid
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
DrugBank
ECHA InfoCard 100.000.703
EC Number 208-220-0
KEGG
UNII
Properties[1]
C5H11NO2
Molar mass 117.15 g·mol−1
Density 1.316 g/cm3
Melting point 298 °C (568 °F; 571 K) (decomposition)
soluble
Acidity (pKa) 2.32 (carboxyl), 9.62 (amino)[2]
-74.3·10−6 cm3/mol
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

Valine (abbreviated as Val or V) encoded by the codons GUU, GUC, GUA, and GUG is an α-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 Hermann Emil Fischer.[3] 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.[4][5]

Nomenclature

According to IUPAC, carbon atoms forming valine are numbered sequentially starting from 1 denoting the carboxyl carbon, whereas 4 and 4' denote the two terminal methyl carbons.[6]

Biosynthesis

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:[7]

  1. Acetolactate synthase (also known as acetohydroxy acid synthase)
  2. Acetohydroxy acid isomeroreductase
  3. Dihydroxyacid dehydratase
  4. Valine aminotransferase

Metabolism of L-Valine

L-Valine --> alpha-Ketoisovaleric acid --> Isobutyryl-CoA --> Methylmalonate semialdehyde --> Methylmalonyl-CoA (a form) -->

Methylmolonyl-CoA (b form) --> Succinyl-CoA , which then can enter the Citric Acid Cycle.

Transamination of Valine is by Glutamate-alpha-ketoisovalerate transaminase, oxidative decarboxylation of the product is like that done to Pyruvate, Vitamin B-12 is a cofactor in the isomerization of Methylmalonyl-CoA to Succinyl-CoA

Source: Biochemistry, 8th edition, by James M. Orten and Otto W. Neuhaus, (1970) pages 367-368.

Requirements

The Food and Nutrition Board (FNB) of the U.S. Institute of Medicine set Recommended Dietary Allowances (RDAs) for essential amino acids in 2002. For valine, foradults 19 years and older, 4 mg/kg body weight/day.[8]

Synthesis

Racemic valine can be synthesized by bromination of isovaleric acid followed by amination of the α-bromo derivative[9]

HO2CCH2CH(CH3)2 + Br2 → HO2CCHBrCH(CH3)2 + HBr
HO2CCHBrCH(CH3)2 + 2 NH3 → HO2CCH(NH2)CH(CH3)2 + NH4Br

Valine and insulin resistance

Valine, as well as other branched-chain amino acids, are associated with insulin resistance, as higher levels of valine are observed in the blood of diabetic mice, rats, and humans.[10] Mice fed a valine deprivation diet for one day have improved insulin sensitivity, and feeding of a valine deprivation diet for one week significantly decreases blood glucose levels.[11] The valine catabolite 3-hydroxyisobutyrate promotes skeletal muscle insulin resistance in mice by stimulating fatty acid uptake into muscle and lipid accumulation.[12] In humans, a protein restricted diet lowers blood levels of valine and decreases fasting blood glucose levels.[13]

Valine and hematopoietic stem cells

Experiments in mice have shown that dietary valine is essential for hematopoietic stem cell self-renewal.[14] Dietary valine restriction selectively depletes long-term repopulating Hematopoietic Stem Cells (HSC) in mouse Bone Marrow (BM). Successful stem cell transplantation was achieved in mice without irradiation after 3 weeks on a -Val diet. Long term survival of the transplanted mice was achieved when valine was returned to the diet gradually over a 2 week period to avoid refeeding syndrome.

See also

References

  1. ↑ 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.
  2. ↑ Dawson, R.M.C., et al., Data for Biochemical Research, Oxford, Clarendon Press, 1959.
  3. ↑ "valine". Encyclopædia Britannica Online. Retrieved 2015-12-06.
  4. ↑ "valine". Merriam-Webster Online Dictionary. Retrieved 2015-12-06.
  5. ↑ "valeric acid". Merriam-Webster Online Dictionary. Retrieved 2015-12-06.
  6. ↑ 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.
  7. ↑ 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..
  8. ↑ Institute of Medicine (2002). "Protein and Amino Acids". Dietary Reference Intakes for Energy, Carbohydrates, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC: The National Academies Press. pp. 589–768.
  9. ↑ Marvel, C. S. (1940). "dl-Valine". Org. Synth. 20: 106.; Coll. Vol., 3, p. 848.
  10. ↑ Lynch, Christopher J.; Adams, Sean H. (2014-12-01). "Branched-chain amino acids in metabolic signalling and insulin resistance". Nature Reviews. Endocrinology. 10 (12): 723–736. ISSN 1759-5037. PMC 4424797 Freely accessible. PMID 25287287. doi:10.1038/nrendo.2014.171.
  11. ↑ Xiao, Fei; Yu, Junjie; Guo, Yajie; Deng, Jiali; Li, Kai; Du, Ying; Chen, Shanghai; Zhu, Jianmin; Sheng, Hongguang (2014-06-01). "Effects of individual branched-chain amino acids deprivation on insulin sensitivity and glucose metabolism in mice". Metabolism: Clinical and Experimental. 63 (6): 841–850. ISSN 1532-8600. PMID 24684822. doi:10.1016/j.metabol.2014.03.006.
  12. ↑ Jang, Cholsoon; Oh, Sungwhan F.; Wada, Shogo; Rowe, Glenn C.; Liu, Laura; Chan, Mun Chun; Rhee, James; Hoshino, Atsushi; Kim, Boa (2016-04-01). "A branched-chain amino acid metabolite drives vascular fatty acid transport and causes insulin resistance". Nature Medicine. 22 (4): 421–426. ISSN 1546-170X. PMID 26950361. doi:10.1038/nm.4057.
  13. ↑ Fontana, Luigi; Cummings, Nicole E.; Arriola Apelo, Sebastian I.; Neuman, Joshua C.; Kasza, Ildiko; Schmidt, Brian A.; Cava, Edda; Spelta, Francesco; Tosti, Valeria (2016-06-21). "Decreased Consumption of Branched-Chain Amino Acids Improves Metabolic Health". Cell Reports. 16: 520–30. ISSN 2211-1247. PMC 4947548 Freely accessible. PMID 27346343. doi:10.1016/j.celrep.2016.05.092.
  14. ↑ Taya, Yuki; Ota, Yasunori; Wilkinson, Adam C.; Kanazawa, Ayano; Watarai, Hiroshi; Kasai, Masataka; Nakauchi, Hiromitsu; Yamazaki, Satoshi (2016-12-02). "Depleting dietary valine permits nonmyeloablative mouse hematopoietic stem cell transplantation". Science. 354 (6316): 1152–1155. doi:10.1126/science.aag3145.
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