What L-Leucine?(abbreviated as Leu or L), L-Leucine is an -amino acid with the chemical formula HO2CCH(NH2)CH2CH(CH3)2. It is an essential amino acid, which means that humans cannot make it within their body. So for the body to get this key amino acid in the system it has to pull them from a variety of foods. 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. Food sources for leucine are: meat, nuts, beans, brown rice, soy flour, whole wheat and eggs.