Valine (symbolVal orV)[4] 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 chainisopropyl group, making it anon-polaraliphatic amino acid. Valine isessential in humans, meaning the body cannot synthesize it; it must be obtained from dietary sources which are foods that containproteins, such as meats, dairy products, soy products, beans and legumes. It isencoded by allcodons starting with GU (GUU, GUC, GUA, and GUG).
Valine was first isolated fromcasein in 1901 byHermann Emil Fischer.[5] The name valine comes from its structural similarity tovaleric acid, which in turn is named after the plantvalerian due to the presence of the acid in the roots of the plant.[6][7]
According toIUPAC, carbon atoms forming valine are numbered sequentially starting from 1 denoting thecarboxyl carbon, whereas 4 and 4' denote the two terminalmethyl carbons.[8]
Valine, like other branched-chain amino acids, is synthesized by bacteria and plants, but not by animals.[9] It is therefore anessential amino acid in animals, and needs to be present in the diet. Adult humans require about 24 mg/kg body weight daily.[10] It is synthesized in plants and bacteria via several steps starting frompyruvic acid. The initial part of the pathway also leads toleucine. The intermediateα-ketoisovalerate undergoesreductive amination withglutamate. Enzymes involved in this biosynthesis include:[11]
Lower levels of serum valine, like other branched-chain amino acids, are associated with weight loss and decreasedinsulin resistance: higher levels of valine are observed in the blood of diabetic mice, rats, and humans.[16] Mice fed a BCAA-deprived diet for one day had improved insulin sensitivity, and feeding of a valine-deprived diet for one week significantly decreases blood glucose levels.[17] In diet-induced obese and insulin resistant mice, a diet with decreased levels of valine and the other branched-chain amino acids resulted in a rapid reversal of the adiposity and an improvement in glucose-level control.[18] The valine catabolite3-hydroxyisobutyrate promotes insulin resistance in mice by stimulating fatty acid uptake into muscle and lipid accumulation.[19] In mice, a BCAA-restricted diet decreased fasting blood glucose levels and improved body composition.[20]
Dietary valine is essential forhematopoietic stem cell (HSC) self-renewal, as demonstrated by experiments in mice.[21] Dietary valine restriction selectively depletes long-term repopulating HSC in mouse bone marrow. Successful stem cell transplantation was achieved in mice without irradiation after 3 weeks on a valine restricted diet. Long-term survival of the transplanted mice was achieved when valine was returned to the diet gradually over a 2-week period to avoidrefeeding syndrome.
^Lehninger, Albert L.; Nelson, David L.; Cox, Michael M. (2000).Principles of Biochemistry (3rd ed.). New York: W. H. Freeman.ISBN1-57259-153-6..
^Mathews CK (2000).Biochemistry. Van Holde, K. E., Ahern, Kevin G. (3rd ed.). San Francisco, Calif.: Benjamin Cummings. p. 776.ISBN978-0-8053-3066-3.OCLC42290721.
^"L-Valine".Stanford Chemicals. Retrieved29 October 2024.
^Xiao F, Yu J, Guo Y, Deng J, Li K, Du Y, et al. (June 2014). "Effects of individual branched-chain amino acids deprivation on insulin sensitivity and glucose metabolism in mice".Metabolism.63 (6):841–50.doi:10.1016/j.metabol.2014.03.006.PMID24684822.
