Valine (abbreviated as Val or V) is an α-amino acid with the chemical formula HO2CCH(NH2)CH(CH3)2. L-Valine is one of 20 proteogenic amino acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as nonpolar. Along with leucine and isoleucine, valine is a branched-chain amino acid. It is named after the plant valerian. In sickle-cell disease, valine substitutes for the hydrophilic amino acid glutamic acid in hemoglobin. Because valine is hydrophobic, the hemoglobin does not fold correctly.
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-ketovalerate 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
Racemic valine can be synthesized by bromination of isovaleric acid
followed by amination of the α-bromo derivative
- HO2CCH2CH(CH3)2 + Br2 → HO2CCHBrCH(CH3)2 + HBr
- HO2CCHBrCH(CH3)2 + 2 NH3 → HO2CCH(NH2)CH(CH3)2 + NH4Br
sources of valine include cottage cheese, fish, poultry, peanuts, sesame seeds, and lentils.