Figure 1.

Anaerobic reduction of 5-NI compounds by PFOR and Fd. 5-NI compounds (R-NO₂) are reduced in an anaerobic cell-free assay by purified Fd, which accepts one electron from PFOR during the decarboxylation of pyruvate.⁹ Reduction of metronidazole and tinidazole can be followed by a decrease in absorbance at 320 nm, but reduction of other 5-NIs is not so readily monitored. In the intact cell and in the absence of 5-NIs, Fd is oxidized by Fd:NAD oxidoreductase with terminal electron acceptors being NAD(P)H:menadione oxidoreductase, DT diaphorase⁵⁰ or NADH oxidases.^51,52