FAC suppresses the catalytic activity of RED but not NQO1. Cytosolic lysates of COS-1 cells transfected with the indicated constructs were assayed for (A) RED activity and (B) NQO1 activity as described (Materials and Methods). The indicated amounts of transfected DNA (μg) were standardized with empty vector DNA to a concentration of 1 μg/mL for a final amount of 5 μg. The mean of at least three independent measurements and the standard error of the mean are shown.