Protective effects of suprofen and its methyl ester against inactivation of rabbit kidney carbonyl reductase by phenylglyoxal

Suprofen (SP) was little reduced by rabbit kidney carbonyl reductase, whereas its methyl ester (SPM) was an efficient substrate of the enzyme. To account for the differential catalytic activities for SP and SPM, the protective effects of these compounds against the inactivation of the enzyme by phenylglyoxal (PGO) were compared. Since the carboxyl group of SP is negatively charged and one essential arginine residue is known to be located in the NADPH-binding site of the enzyme, the protection of SP against the inactivation of the enzyme by PGO is expected to be more effective than that of SPM lacking a carboxyl group. However, the protective effects of SP and SPM were very similar. These results suggest that in spite of evidence for the binding of SP to the coenzyme-binding site, the carboxyl group of SP fails to interact with one essential arginine residue located in the site.