Isoleucine is an amino acid. This amino acid cannot be made by humans so it has to be ingested. The codons that code for this amino acid are AUU AUC AUA.
Four sterioisomers of isoleucine are possible, but it is only found as 2S,3S)-2-amino-3-methylpentanoic acid
Isoleucine can also be made to use glucose.