Dietary leucine Īs a food additive, L-leucine has E number E641 and is classified as a flavor enhancer. Leucine and β-hydroxy β-methylbutyric acid, a minor leucine metabolite, exhibit pharmacological activity in humans and have been demonstrated to promote protein biosynthesis via the phosphorylation of the mechanistic target of rapamycin (mTOR). It is the most important ketogenic amino acid in humans. The primary metabolic end products of leucine metabolism are acetyl-CoA and acetoacetate consequently, it is one of the two exclusively ketogenic amino acids, with lysine being the other. Like valine and isoleucine, leucine is a branched-chain amino acid. It is encoded by the codons UUA, UUG, CUU, CUC, CUA, and CUG. Human dietary sources are foods that contain protein, such as meats, dairy products, soy products, and beans and other legumes. It is essential in humans, meaning the body cannot synthesize it: it must be obtained from the diet. Leucine is an α-amino acid, meaning it contains an α- amino group (which is in the protonated −NH 3 + form under biological conditions), an α- carboxylic acid group (which is in the deprotonated −COO − form under biological conditions), and a side chain isobutyl group, making it a non-polar aliphatic amino acid. Leucine (symbol Leu or L) is an essential amino acid that is used in the biosynthesis of proteins.
