Alanine (abbreviated as Ala or A) is an ?-amino acid with the chemical formula CH3CH(NH2)COOH. The L-isomer is one of the 22 proteinogenic amino acids, i.e. the building blocks of proteins. Its codons are GCU, GCC, GCA, and GCG. It is classified as a nonpolar amino acid. L-alanine is second only 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.