Leucine is one of the 20 most common amino acids and coded for by DNA. It is isomeric with isoleucine. Nutritionally, in humans, leucine is an essential amino acid.
Leucine is the most common amino acid found in proteins, and is essential for optimal growth in infancy and childhood and for nitrogen equilibrium in adults. It is suspected that Leucine plays a part in maintaining muscles by equalizing synthesis and breakdown of proteins.