Isoleucine

L-Isoleucine
IUPAC name Isoleucine
Other names 2-Amino-3-methylpentanoic acid
Identifiers
CAS number	73-32-5 Y
PubChem	791
SMILES CC[C@H](C)[C@H](N)C(O)=O
Properties
Molecular formula	C6H13NO2
Molar mass	131.17 g mol−1
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

Isoleucine (abbreviated as Ile or I)^[1] is an α-amino acid with the chemical formula HO₂CCH(NH₂)CH(CH₃)CH₂CH₃. 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.

With a hydrocarbon side chain, isoleucine is classified as a hydrophobic amino acid. Together with threonine, isoleucine is one of two common amino acids that have a chiral side chain. Four stereoisomers of isoleucine are possible, including two possible diastereomers of L-isoleucine. However, isoleucine present in nature exists in one enantiomeric form, (2S,3S)-2-amino-3-methylpentanoic acid.

Biosynthesis

As an essential amino acid, isoleucine is not synthesized in animals, hence it must be ingested, usually as a component of proteins. In plants and microorganisms, it is synthesized via several steps, starting from pyruvic acid and alpha-ketoglutarate. Enzymes involved in this biosynthesis include:^[2]

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

Catabolism

Isoleucine is both a glucogenic and a ketogenic amino acid. After transamination with alpha-ketoglutarate the carbon skeleton can be converted into either Succinyl CoA, and fed into the TCA cycle for oxidation or conversion into oxaloacetate for gluconeogenesis (hence glucogenic). It can also be converted into Acetyl CoA and fed into the TCA cycle by condensing with oxaloacetate to form citrate. In mammals Acetyl CoA cannot be converted back to carbohydrate but can be used in the synthesis of ketone bodies or fatty acids, hence ketogenic.

Nutritional Sources

Even though this amino acid is not produced in animals, it is stored in high quantities. Foods that have high amounts of isoleucine include eggs, soy protein, seaweed, turkey, chicken, lamb, cheese, and fish. It is obviously not scarce. ^[3]

Isomers of isoleucine

L-isoleucine (2S,3S) and D-isoleucine (2R,3R)

L-allo-isoleucine (2S,3R) and D-allo-isoleucine (2R,3S)

Synthesis

Isoleucine can be synthesized in a multistep procedure starting from 2-bromobutane and diethylmalonate.^[4] Synthetic isoleucine was originally reported in 1905.^[5]

References

1. ↑ IUPAC-IUBMB Joint Commission on Biochemical Nomenclature. "Nomenclature and Symbolism for Amino Acids and Peptides". Recommendations on Organic & Biochemical Nomenclature, Symbols & Terminology etc. http://www.chem.qmul.ac.uk/iupac/AminoAcid/. Retrieved 2007-05-17. 
2. ↑ Nelson, D. L.; Cox, M. M. "Lehninger, Principles of Biochemistry" 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6.
3. ↑ [1], List is in order of highest to lowest of per 200 Calorie serving of the food, not volume or weight.
4. ↑ "dl-Isoleucine", Org. Synth., 1955, http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv3p0495 ; Coll. Vol. 3: 495 
5. ↑ Bouveault and Locquin, Compt. rend., 141, 115 (1905).

External links

• Food Sources of Isoleucine
• Isoleucine and valine biosynthesis