In vitro interaction of penicillins and cephalosporins with human placenta GSH S-transferase.

Human purified placenta GSH S-transferase was generally inhibited by penicillins and cephalosporins to a different extent. Among the seven penicillins tested the dihalogenate dicloxacillin and flucloxacillin were the strongest inhibitors. All cephalosporins showed competitive inhibition for the electrophilic substrate, while penicillins acted as non-competitive inhibitors. Exposure of the enzyme to cephalosporins led to the loss of the catalytic activity. Addition of reduced glutathione in the incubation system would induce the formation of a conformational state of the enzyme which prevents cephalosporins binding.