Isoleucine is an amino acid found in proteins. In mammals, isoleucine is an essential amino acid, meaning it must be present in the diet. Isoleucine's nonpolar side chain classifies it as an aliphatic amino acid.

The more hydrophobic amino acids, like isoleucine, are usually found in the interior of a protein molecule, where they are shielded from water.

One Letter Code	Three Letter Code	Molecular Wt. (Daltons)	Genetic Code Codons
I	ILE	113.17	AUU, AUC, AUA