"Leucine (abbreviated as Leu or L)[2] is a branched-chain α-amino acid with the chemical formula 
HO2CCH(NH2)CH2CH(CH3)2. Leucine is classified as a hydrophobic amino acid due to its aliphatic isobutyl side chain. It is encoded by six codons (UUA, UUG, CUU, CUC, CUA, and CUG) and is a major component of the subunits in ferritin, astacin and other 'buffer' proteins. Leucine is an essential amino acid."
"As an essential amino acid, leucine is unable to be synthesised by animals. Consequently, it must be ingested, usually as a component of proteins. In plants and microorganisms, leucine is synthesised from pyruvic acid by a series of enzymes."
"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."