Lactate racemase. Hydroxylamine-dependent 18O exchange of the alpha-hydroxyl of lactic acid.

The lactic acid racemase (EC 5.1.2.1) derived from Clostridium butylicum catalyzes the racemization of the alpha-18O label. The proposed alpha-carbonyl intermediate for the enzyme-catalyzed reaction has been previously shown to be trapped as an enzyme-bound oxime in the presence of hydroxylamine. This report demonstrates that the formation of the inactive enzyme-bound oxime, followed by reactivation in the presence of an excess of competing free carbonyl (pyruvic acid) results in a complete loss of the alpha-18O label from an original alpha-18O-labeled lactic acid.