A comparative study on 1-nitropyrene and nitrofurazone reductases in Escherichia coli

1-Nitropyrene and nitrofurazone reductases in Escherichia coli B/r were studied comparatively. Nitrofurazone reductase activity was oxygen-insensitive, whereas 1-nitropyrene reductase activity was markedly inhibited by oxygen in both intact cells and cell-free preparations. The former activity depended upon reduced nicotinamide adenine dinucleotide or reduced nicotinamide adenine dinucleotide phosphate, whereas the latter activity upon flavin-adenine dinucleotide (FAD) as well as the reduced pyridine nucleotide. E. coli B/r acquired resistance to nitrofurazone in two mutational steps, associated with stepwise loss of the oxygen-insensitive nitrofuran reductase activity. However, 1-nitropyrene reductases were not affected at all by the mutation. These facts indicated that the major enzymes responsible for the reduction of 1-nitropyrene and nitrofurazone in E. coli B/r were different from each other. 1-Nitropyrene reductases were resolved by diethylaminoethyl-cellulose column chromatography into four enzymes all of which seem to reduce FAD, too. Among them, three enzymes appear to be able also to catalyze the reduction of nitrofurazone under anaerobic conditions.