Tight-binding inhibition kinetics of warfarin. (A) Warfarin inhibition curves at different concentrations of microsomal VKORC1. The concentration of total microsome proteins and that of the VKOR protein in microsomes (estimated in panel B) are indicated. Error bars are from 3 repeats. (B) Estimation of microsomal VKORC1 concentration. Series dilutions of total microsome proteins and purified protein are compared. (C) Correlation between warfarin IC₅₀ and estimated microsomal VKORC1 concentration. (D) Effective VKORC1 concentration determined from extrapolation of the linear part of Morrison curves. The green circles in panels A and D exemplify that estimated (from panel B) and effective VKOR concentrations are similar.