leucine

Leucine
IUPAC name	Leucine
Other names	2-Amino-4-methylpentanoic acid
Identifiers
CAS number	61-90-5 Y
PubChem	6106
SMILES	CC(C)C[C@H](N)C(O)=O
Properties
Molecular formula	C6H13NO2
Molar mass	131.17 g mol−1
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Y (what is this?)  (verify) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Leucine (abbreviated as Leu or L)^[1] is an α-amino acid with the chemical formula HO₂CCH(NH₂)CH₂CH(CH₃)₂. It is an essential amino acid, which means that humans cannot synthesise it. Its codons are UUA, UUG, CUU, CUC, CUA, and CUG. With a hydrocarbon side chain, leucine is classified as a hydrophobic amino acid. It has an isobutyl R group. Leucine is a major component of the sub units in ferritin, astacin and other 'buffer' proteins.

Biosynthesis

As an essential amino acid, leucine is not synthesized in animals, hence it must be ingested, usually as a component of proteins. It is synthesized in plants and microorganisms via several steps starting from pyruvic acid. The initial part of the pathway also leads to valine. The intermediate α-ketovalerate is converted to α-isopropylmalate and then β-isopropylmalate, which is dehydrogenated to α-ketoisocaproate, which in the final step undergoes reductive amination. Enzymes involved in a typical leucine biosynthesis include^[2]

• Acetolactate synthase,
• Acetohydroxy acid isomeroreductase,
• Dihydroxyacid dehydratase,
• α-Isopropylmalate synthase,
• α-Isopropylmalate isomerase,
• Leucine aminotransferase.

Biology

As a dietary supplement, leucine has been found to slow the degradation of muscle tissue by increasing the synthesis of muscle proteins in aged rats.^[3] Leucine is utilized in the liver, adipose tissue, and muscle tissue. In adipose and muscle tissue, leucine is used in the formation of sterols, and the combined usage of leucine in these two tissues is seven times greater than its use in the liver.^[4]

Leucine toxicity, as seen in decompensated Maple Syrup Urine Disease (MSUD), causes delirium and neurologic compromise, and can be life-threatening.

In yeast genetics, mutants with a defective gene for leucine synthesis (leu2) are transformed with a plasmid that contains a working leucine synthesis gene (LEU2) and grown on minimal media. Leucine synthesis then becomes a useful selectable marker.

Dietary aspects

Betaines

(S)-Leucine (left) and (R)-leucine (right) in zwitterionic form at neutral pH

Chemical properties

Leucine is a branched-chain amino acid (BCAA) since it possesses an aliphatic side-chain that is non-linear.

Racemic leucine had been subjected to circularly polarized synchrotron radiation in order to better understand the origin of biomolecular asymmetry. An enantiomeric enhancement of 2.6 % had been induced, indicating a photochemical origin of biomolecules' homochirality.^[6]

Food additive

As a food additive, L-Leucine has E number E641 and is classified as a flavour enhancer.

See also

• Leucines, description of the isomers of leucine
• Photo-reactive leucine

References

External links

• Leucine biosynthesis
• Leucine content in food
• Computational Chemistry Wiki
• Leucine prevents muscle loss in rats
• Leucine helps regulate appetite in rats
• Combined ingestion of protein and free leucine with carbohydrate increases postexercise muscle protein synthesis in vivo in male subjects
• A leucine-supplemented diet restores the defective postprandial inhibition of proteasome-dependent proteolysis in aged rat skeletal muscle