MECHANISM-BASED INACTIVATION OF MANDELATE RACEMASE BY PROPARGYLGLYCOLATE

Propargylglycolate (2-hydroxy-3-butynoic acid) has been determined to be both a substrate and an inactivator of mandelate racemase. The partition ratio for racemization/inactivation has been estimated to be approximately 17,000. Inactivation of the racemase appears to require the rapid covalent addition of 1 substrate molecule; however, a slower labeling process is observed that results in the attachment of up to 5 molecules of substrate per active site. The process is consistent with an enzyme-catalyzed rearrangement of the acetylenic substrate to an allenic-enol that affords 2-keto-3-butenoate as the ultimate electrophile.