Reductase enzymes during decolorization The azo reductase activity was assayed by modifying earlier method (23); monitoring the decrease in the Methyl Red concentration at 440 nm in a reaction mixture of 2.2 ml containing 152 mM Methyl Red, 50 mM sodium phosphate buffer (pH 5.5) and 20 mM NADH.
Enzyme activity was calculated by using molar extinction coefficient of Methyl Red.
NADHeDCIP reductase activity was assayed by following the procedures reported earlier (11).
Riboflavin reductase NAD(P)H:flavin oxidoreductase was measured by the method of Fontecave et al. (24) with some modification. In this aerobic assay, the flavin reductase catalyzes the reduction of riboflavin, and the reduced riboflavin is
immediately reoxidized by oxygen.
Cell extract was added to a solution (final volume, 1 ml) containing 100 mM of TriseHCl (pH 7.5), 25 mmol of NADPH and
0.003 unit riboflavin. The decrease in absorbance at 340 nm (A340) was measured spectrophotometrically.
Reaction rates were calculated by using a molar extinction coefficient of 6.3 mM cm1.
One unit of enzyme activity was defined as mg of riboflavin reduced min/mg protein. All enzyme assays were run in triplicate.