Nitroreductases in the Madagascar cockroach,Gromphadorhina portentosa

Nitrobenzene reduction by tissue preparations of the Madagascar cockroach, Grompphadorhina portentosa, was studied in vitro. Active enzyme preparations were obtained from midgut, hindgut, fat body, and Malpighian tubules. Anaerobic conditions were essential for activity which was found in all subcellular fractions tested. The microsomal enzymes were strongly NADPH-dependent whereas the soluble enzymes were strongly NADH-dependent. Flavin addition stimulated activity greatly and it appeared that the true substrate for the nitroreductases was FMN and that nitrobenzene was nonenzymatically reduced by FMH₂.