[ Branched-chain amino acid, BCAA ]
An amino acid having aliphatic side-chains with a branch. The three proteinogenic branched-chained amino acids are leucine, isoleucine and valine. Non-proteinogenic BCAAs include 2-aminoisobutyric acid.
The three proteinogenic BCAAs are among the nine essential amino acids for humans, accounting for 35% of the essential amino acids in muscle proteins and 40% of the preformed amino acids required by mammals.