Alanine (symbol Ala or A) is an ±-amino acid that is used in the biosynthesis of proteins. It contains an ±-amino group (which is in the protonated form, NH3+, under biological conditions), an ±-carboxylic acid group (which is in the deprotonated form, COO , under biological conditions), and a side chain methyl group, making it a nonpolar, aliphatic amino acid. It is non-essential in humans: because the body can synthesize it, it does not need to be present in the diet. It is encoded by all codons starting with GC (GCU, GCC, GCA, and GCG).
The L-isomer of alanine (left-handed) is the one that is incorporated into proteins. L-Alanine is second only to leucine in rate of occurrence, accounting for 7.8% of the primary structure in a sample of 1,150 [human?][clarification needed] proteins. The right-handed form, D-Alanine occurs in polypeptides in some bacterial cell wallsp. 131 and in some peptide antibiotics, and occurs in the tissues of many crustaceans and molluscs as an osmolyte.