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Chemical structure of Isoleucine
Chemical structure of Isoleucine
IUPAC name
Other names
2-Amino-3-methylpentanoic acid
73-32-5 YesY
ChEBI CHEBI:58045 YesY
ChemSpider 6067 YesY
DrugBank DB00167 YesY
Jmol interactive 3D Image
KEGG D00065 YesY
PubChem 791
UNII 04Y7590D77 YesY
Molar mass 131.18 g·mol−1
Supplementary data page
Refractive index (n),
Dielectric constantr), etc.
Phase behaviour
YesY verify (what is YesYN ?)
Infobox references

Isoleucine (abbreviated as Ile or I) is a proteinogenic α-amino acid which is essential in humans (it cannot be synthesized, so it must be ingested). The iso- in its name refers to it being an isomer of leucine.[1] Its chemical formula is HO2CCH(NH2)CH(CH3)CH2CH3. Its codons are AUU, AUC and AUA. With a hydrocarbon side chain, isoleucine is classified as hydrophobic. 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.



As an essential nutrient, it is not synthesized in the body, 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


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 converted 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.

Biotin, sometimes referred to as Vitamin B7 or Vitamin H, is an absolute requirement for the full catabolism of isoleucine (as well as leucine). Without adequate biotin, the human body will be unable to fully break down isoleucine and leucine molecules.[3] This can lead to numerous physiological issues (related to muscle maintenance and protein synthesis, lipid metabolism, and fatty acid metabolism) as well as cognitive issues resulting from general metabolic pathway failure and the irritating effects of hydroxyisovalerate, a byproduct of incomplete isoleucine catabolism. Isovaleric acidemia is an example of a disorder caused by incomplete catabolism of leucine.[citation needed]

Nutritional Sources[edit]

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.[4]

Isomers of isoleucine[edit]

Forms of Isoleucine
Common name: isoleucine D-isoleucine L-isoleucine DL-isoleucine allo-D-isoleucine allo-L-isoleucine allo-DL-isoleucine
Synonyms: (R)-Isoleucine L(+)-Isoleucine (R*,R*)-isoleucine alloisoleucine
PubChem: CID 791 from PubChem CID 94206 from PubChem CID 6306 from PubChem CID 76551 from PubChem
EINECS number: 207-139-8 206-269-2 200-798-2 216-143-9 216-142-3 221-464-2
CAS number: 443-79-8 319-78-8 73-32-5 1509-35-9 1509-34-8 3107-04-8
L-Isoleucin - L-Isoleucine.svg D-isoleucine.svg
L-isoleucine (2S,3S) and D-isoleucine (2R,3R)
L-alloisoleucine.svg D-alloisoleucine.svg
L-allo-isoleucine (2S,3R) and D-allo-isoleucine (2R,3S)


Isoleucine can be synthesized in a multistep procedure starting from 2-bromobutane and diethylmalonate.[5] Synthetic isoleucine was originally reported in 1905.[6]

German chemist Felix Ehrlich discovered isoleucine in hemoglobin in 1903.


  1. ^ Journal of the Chemical Society. LXXXIV (part i): 796. 1903. The author has isolated leucine and a new compound, d-isoleucine, isomeric with it. d-isoLeucine crystallises in shining rods or leaflets.  Missing or empty |title= (help)
  2. ^ Nelson, D. L.; Cox, M. M. "Lehninger, Principles of Biochemistry" 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6.
  3. ^ "Biotin & Detoxification Needs in Cognitively Delayed Adult - Metametrix Learning Center". Retrieved 2013-10-18. 
  4. ^ [1], List is in order of highest to lowest of per 200 Calorie serving of the food, not volume or weight.
  5. ^ "dl-Isoleucine". Org. Synth. 1955. ; Coll. Vol. 3, p. 495 
  6. ^ Bouveault and Locquin, Compt. rend., 141, 115 (1905).

External links[edit]