Figure 4.

Metronidazole reduction assay. MTZ reductase activity was determined under anaerobic conditions as described in the text. The enzymatic activities were monitored spectrophotometrically at 23^oC, by following the decrease in absorbance at 320 nm resulting from reduction of MTZ (ε=9.0 mM⁻¹ cm⁻¹) and oxidation of NAD(P)H (ε=4.5 mM⁻¹ cm⁻¹). Results reported for MTZ reduction are corrected for the contribution of NAD(P)H oxidation using a combined molar extinction coefficient (ε_MTZ +2ε_NAD(P)H = 18.0 mM⁻¹ cm⁻¹). No activity was observed in the absence of enzyme or NAD(P)H. Three replicates were performed for each experiment.