NADPH-dependency assays of 78FF and 5H78FF inhibition of P450s 1A1, 1A2, and 1B1: (black curves) blank control, the time-course curve of enzymatic reaction without an inhibitor; (light-gray curves) preincubation without NADPH, the time-course curve of enzymatic reaction with 10 nM 78FF or 5H78FF in the absence of 5 min NADPH preincubation; (medium-gray curves) preincubation with NADPH, the time-course curve of enzymatic reaction with 10 nM 78FF or 5H78FF in the presence of 5 min NADPH preincubation. For the assays on P450s 1A1 and 1B1, 10 nM 78FF or 5H78FF does not influence the enzymatic activities with or without NADPH preincubation. For the assays on P450 1A2, 10 nM 78FF or 5H78FF exhibits a significant inhibition toward the enzyme without NADPH preincubation, while 10 nM 78FF or 5H78FF exhibits >90% inhibition toward the enzyme with NADPH preincubation. This suggests that 78FF and 5H78FF inactivate P450 1A2 NADPH-dependently.