A proof-of-concept receptor-based assay for sulfonamides.

The gene encoding the dihydropteroate synthase (DHPS) of Streptococcus pneumonia has been cloned, sequenced, and expressed in Escherichia coli. The protein has been purified and used to develop a novel microplate assay for the detection of sulfonamides. The assay was based on the competition between sulfonamides and horseradish peroxidase (HRP)-labeled sulfonamide derivative, 4-(4-aminobenzenesulfonylamino) benzoic acid (CS) for the immobilized protein. Under optimized conditions, nine sulfonamides and p-aminobenzoic acid (PABA) could be detected below 100 ng/ml and 28 sulfonamides used in the study could be detected with IC50 values ranging from 426 to 50,000 ng/ml. It is concluded that this method offers a robust and rapid alternative to other methods for the screening of sulfonamides.