Effect of exogenous flavin cofactor on the activities of recombinant NOX in soluble form. Before purification, crude extracts were incubated with different flavin nucleotides at different concentrations (from 0 to 150 μM of either FMN or FAD). Activity was determined in 50 mM sodium phosphate at pH 7 and 37°C. Soluble enzyme with FAD (triangles), soluble enzyme with FMN (circles). The relative activity was calculated taking as fraction 1 the initial observed activity without flavin cofactor.