any one enzyme of the isomerase class that catalyzes the reversible interconversions of stereoisomers having one asymmetric carbon atom. Racemases include the enzymes that catalyze the interconversion of L- and D-amino acids, Land D-hydroxy acids, and the derivatives of these acids; for example, the interconversion of L- and D-alanine is catalyzed by alanine racemase, and the interconversion of L- and D-lactic acid by lactate racemase.

The racemases of amino acids are conjugated proteins having pyridoxal phosphate as the coenzyme. Thus far, the bacterial racemases of alanine, methionine, proline, glutamic acid, lysine, and threonine having been the most carefully studied. The racemase of lysine is used in the industrial production of L-lysine.