It is classified as a non-polar, uncharged (at physiological pH), branched-chain, aliphatic amino acid. It contains an α-amino group (which is in the protonated −NH + 3 form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −COO − form under biological conditions), and a hydrocarbon side chain with a branch (a central carbon atom bound to three other carbon atoms). Isoleucine (symbol Ile or I) is an α-amino acid that is used in the biosynthesis of proteins.
