293 cells that have warfarin-resistant quinone reductase activity do not show differences in inhibition of KO reduction and fIX carboxylation. (A) r-FIX 293 cells were generated by transfection of human r-fIX in pCMV6-A-Puro (Origene) and selection with puromycin (1 µg/mL). A clonal isolate was tested for warfarin inhibition as in Figure 3A, revealing the presence of warfarin-resistant quinone reductase activity. (B) Warfarin sensitivity of KO reduction and fIX carboxylation were analyzed as in Figure 3C.