Inhibition curves for warfarin assessed in DKO cells. Exogenous VKR activity determined in DKO cells and assessed by overexpression of VKOR variants and F9. (A) Warfarin dose-response curves for VKORC1, VKORC1L1, and loop swap variants. (B) Warfarin dose-response curves for arginine variants of VKORC1L1. Measurements were performed in triplicates, values are shown as mean and error bars are represented as standard error of the mean. The coefficient of determination (R²) calculated for each inhibition curve: (A) VKORC1, R² = 0.9935; VKORC1L1, R² = 0.9628; VKORC1 loop swap L1, R² = 0.9826. (B) VKORC1L1, R² = 0.9628; Arg38Glu, R² = 0.9715; Arg42Glu, R² = 0.9875; Arg38Glu+ Arg42Glu, R² = 0.9140. (C-D) Expression of all VKOR variants detected by α-myc antibody (vertical lines have been inserted to indicate a repositioned gel lane). As loading control, α-ERGIC-53 was used.