Studies on Oxygen-Insensitive Nitrofuran Reductase in Escherichia coli B/r

Oxygen-insensitive nitrofuran reductase in Escherichia coli B/r was clearly resolved by DEAE-cellulose column chromatography into two components, one NADPH-linked, and the other both NADPH- and NADH-linked. It is known that the strain acquires resistance to nitrofurazone in two mutational steps. In such a case, the first step mutants had no NADPH-linked component and the second step ones had neither this component nor the NAD(P)H-linked one. The NADPH- and NADH-linked activities of the latter component were similarly inactivated by heat or urea treatment. In addition, it was found that these activities were significantly inhibited by dicoumarol, an NAD(P)H dehydrogenase inhibitor, to similar extents. These results suggest that the activities of the NAD(P)H-linked component originate from a single enzyme. On the other hand, the NADPH-linked component was less sensitive to heat, urea and dicoumarol.