Symbol: Ile I
Molecular Weight: 131.17
Isolectric point (pH) 5.94
Molecular Formula: C ₆H₁₃N O₂

Isoleucine is one of the 20 most common natural amino acids, coded for in DNA. Its chemical composition is identical to that of leucine, but the arrangement of its atoms is slightly different resulting in different properties. Isoleucine is a member of the aliphatic side-chain amino acid family that is composed of extremely hydrophobic biochemicals that are found principally in the interior of proteins and enzymes. Like several other members of this family (valine and leucine), isoleucine is an essential amino acid that is not synthesized by mammalian tissues. Another feature of this class of amino acids is that they appear to have no other significant biological role than incorporation into proteins and enzymes, where their main purpose is to help dictate the tertiary structure of the macromolecules. Isoleucine as with other branched amino acids appear to promote muscle recovery after physical exercise.