2.5. Enzyme activity assay
Assays were carried out in cuvettes with a total volume of 1 mL. One unit of enzyme activity was defined as the amount of enzyme that transformed 1 mol of substrate per minute (=1 unit = 1 U). The azoreductase assays were performed as described by Pricelius et al.(2007). The reaction mixture contained 400 L of 50 mM sodium phosphate buffer (pH 7.0), 200 L of the sample and 200 L of dye(100 mg/L). The reaction was initiated by the addition of 200 LNADH (7.09 mg/mL, final concentration 2 mM) and followed photo-metrically at 600 nm using a Shimadzu model spectrophotometer.The slope of the initial linear decrease of absorption was used to calculate the enzyme activity.