Valine
Encyclopedia
Valine is an α-amino acid
with the chemical formula
HO2CCH(NH2)CH(CH3)2. L-Valine is one of 20 proteinogenic amino acid
s. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid
is classified as nonpolar. Human dietary sources include cottage cheese, fish, poultry, peanuts, sesame seeds, and lentils.
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.
. 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:
valine can be synthesized by bromination of isovaleric acid
followed by amination of the α-bromo derivative
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
with the chemical formula
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
HO2CCH(NH2)CH(CH3)2. L-Valine is one of 20 proteinogenic amino acid
Proteinogenic amino acid
Proteinogenic amino acids are those amino acids that can be found in proteins and require cellular machinery coded for in the genetic code of any organism for their isolated production. There are 22 standard amino acids, but only 21 are found in eukaryotes. Of the 22, 20 are directly encoded by...
s. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid
Essential amino acid
An essential amino acid or indispensable amino acid is an amino acid that cannot be synthesized de novo by the organism , and therefore must be supplied in the diet.-Essentiality vs. conditional essentiality in humans:...
is classified as nonpolar. Human dietary sources include cottage cheese, fish, poultry, peanuts, sesame seeds, and lentils.
Along with leucine
Leucine
Leucine is a branched-chain α-amino acid with the chemical formula HO2CCHCH2CH2. Leucine is classified as a hydrophobic amino acid due to its aliphatic isobutyl side chain. It is encoded by six codons and is a major component of the subunits in ferritin, astacin and other 'buffer' proteins...
and isoleucine
Isoleucine
Isoleucine is an α-amino acid with the chemical formula HO2CCHCHCH2CH3. It is an essential amino acid, which means that humans cannot synthesize it, so it must be ingested. Its codons are AUU, AUC and AUA....
, valine is a branched-chain amino acid
Branched-chain amino acids
A branched-chain amino acid is an amino acid having aliphatic side-chains with a branch...
. It is named after the plant valerian
Valerian (herb)
Valerian is a hardy perennial flowering plant, with heads of sweetly scented pink or white flowers which bloom in the summer months. Valerian flower extracts were used as a perfume in the sixteenth century....
. In sickle-cell disease
Sickle-cell disease
Sickle-cell disease , or sickle-cell anaemia or drepanocytosis, is an autosomal recessive genetic blood disorder with overdominance, characterized by red blood cells that assume an abnormal, rigid, sickle shape. Sickling decreases the cells' flexibility and results in a risk of various...
, valine substitutes for the hydrophilic amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
glutamic acid
Glutamic acid
Glutamic acid is one of the 20 proteinogenic amino acids, and its codons are GAA and GAG. It is a non-essential amino acid. The carboxylate anions and salts of glutamic acid are known as glutamates...
in hemoglobin
Hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...
. Because valine is hydrophobic, the hemoglobin does not fold
Protein folding
Protein folding is the process by which a protein structure assumes its functional shape or conformation. It is the physical process by which a polypeptide folds into its characteristic and functional three-dimensional structure from random coil....
correctly.
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 acidPyruvic acid
Pyruvic acid is an organic acid, a ketone, as well as the simplest of the alpha-keto acids. The carboxylate ion of pyruvic acid, CH3COCOO−, is known as pyruvate, and is a key intersection in several metabolic pathways....
. The initial part of the pathway also leads to leucine
Leucine
Leucine is a branched-chain α-amino acid with the chemical formula HO2CCHCH2CH2. Leucine is classified as a hydrophobic amino acid due to its aliphatic isobutyl side chain. It is encoded by six codons and is a major component of the subunits in ferritin, astacin and other 'buffer' proteins...
. The intermediate α-ketoisovalerate undergoes reductive amination with glutamate. Enzymes involved in this biosynthesis include:
- Acetolactate synthaseAcetolactate synthaseThe acetolactate synthase enzyme is a protein found in plants and micro-organisms. ALS catalyzes the first step in the synthesis of the branched-chain amino acids ....
(also known as acetohydroxy acid synthase) - Acetohydroxy acid isomeroreductase
- Dihydroxyacid dehydratase
- Valine aminotransferase
Synthesis
RacemicRacemic
In chemistry, a racemic mixture, or racemate , is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule. The first known racemic mixture was "racemic acid", which Louis Pasteur found to be a mixture of the two enantiomeric isomers of tartaric acid.- Nomenclature :A...
valine can be synthesized by bromination of isovaleric acid
3-Methylbutanoic acid
3-Methylbutanoic acid, or more commonly isovaleric acid, is a natural fatty acid found in a wide variety of plants and essential oils. Isovaleric acid is clear colorless liquid that is sparingly soluble in water, but extremely soluble in most common organic solvents.Isovaleric acid has a strong...
followed by amination of the α-bromo derivative
- HO2CCH2CH(CH3)2 + Br2BromineBromine ") is a chemical element with the symbol Br, an atomic number of 35, and an atomic mass of 79.904. It is in the halogen element group. The element was isolated independently by two chemists, Carl Jacob Löwig and Antoine Jerome Balard, in 1825–1826...
→ HO2CCHBrCH(CH3)2 + HBrHydrogen bromideHydrogen bromide is the diatomic molecule HBr. HBr is a gas at standard conditions. Hydrobromic acid forms upon dissolving HBr in water. Conversely, HBr can be liberated from hydrobromic acid solutions with the addition of a dehydration agent, but not by distillation. Hydrogen bromide and... - HO2CCHBrCH(CH3)2 + 2 NH3 → HO2CCH(NH2)CH(CH3)2 + NH4Br