Conversion of NfsA, the major Escherichia coli nitroreductase, to a flavin reductase with an activity similar to that of Frp, a flavin reductase in Vibrio harveyi, by a single amino acid substitution.

NfsA is the major oxygen-insensitive nitroreductase of Escherichia coli, similar in amino acid sequence to Frp, a flavin reductase of Vibrio harveyi. Here, we show that a single amino acid substitution at position 99, which may destroy three hydrogen bonds in the putative active center, transforms NfsA from a nitroreductase into a flavin reductase that is as active as the authentic Frp and a tartrazine reductase that is 30-fold more active than wild-type NfsA.