Leucine (Leu)

Leucine is a branched-chain α-amino acid with the chemical formula HO₂CCH(NH₂)CH₂CH(CH₃)₂. It is an essential amino acid, which means that humans cannot synthesize it. Its codons are UUA, UUG, CUU, CUC, CUA, and CUG. With a hydrocarbon side chain, leucine is classified as a hydrophobic amino acid. It has an isobutyl R group. Leucine is a major component of the sub units in ferritin, astacin and other 'buffer' proteins.

Leucine is utilized in the liver, adipose tissue, and muscle tissue. In adipose and muscle tissue, leucine is used in the formation of sterols, and the combined usage of leucine in these two tissues is seven times greater than its use in the liver. Leucine is the only dietary protein that has the capacity to stimulate muscle protein synthesis.