Isoleucine is one of the three branched-chain amino acids (BCAAs) along with leucine and valine. Isoleucine is stronger than valine but much weaker than leucine in its ability to enhance muscle protein synthesis. Isoleucine, however, promotes cellular glucose uptake and consumption far greater than the other BCAAs (1). Not only can isoleucine be found in BCAA products but also in common foods like meat. Because the isoleucine in meat is bioactive, it should account for your daily intake. 

1.Doi M, et al. Isoleucine, a potent plasma glucose-lowering amino acid, stimulates glucose uptake in C2C12 myotubes. Biochem Biophys Res Commun. (2003)