Alanine racemase (EC 5.1.1.1) [1] catalyzes the pyridoxal-dependent conversion of L-alanine into D-alanine, a key building block of bacterial peptidoglycan. In bacteria such as Escherichia coli or Salmonella typhimurium, there are two forms of alanine racemase: a biosynthetic form (alr) required for cell wall formation and a form (dadB) that functions in L-alanine catabolism. In contrast to dadB and alr which are monomeric enzymes, the alanine racemase of Bacillaceae are homodimers.

The pyridoxal-phosphate group of alanine racemase is attached to a lysine residue. The sequence around this residue is highly conserved in all forms of the enzyme.