Alanine (Ala, A), or 2-aminopropanoic acid, is a non-essential alpha-amino acid. It exists as two distinct enantiomers – L-Alanine and D-Alanine. L-Alanine is one of the 20 amino acids most widely used in protein synthesis, second to leucine, accounting for 7.8% of the primary structure in a sample of 1,150 proteins. D-Alanine occurs in bacterial cell walls and in some peptide antibiotics.