FVII activation by FXa determined by western blotting and FVIIa amidolytic activity. (A) Equivalent molar concentrations (0.5 nM) of WT, R147A, K192A, and R147A/K192A were incubated with 60-nM FXa for 0 and 30 minutes at 37°C. At each time point, the enzymatic reactions were quenched with the reducing sample buffer, run on 12% SDS-PAGE, transferred to PVDF membrane, and probed with the rabbit anti–FVII monoclonal antibody as described in the Methods section. FVIIa LC, the light chain of protease FVIIa; rFVIIa, recombinant FVIIa (NovoSeven, 10 ng). (B) FVII (15 nM) was activated by FXa in reaction buffer at 37°C in the presence of 60-nM FXa for 30 minutes. Rivaroxaban (120 nM) was then added to the inhibit activity of FXa at 37°C for 30 minutes. FVIIa substrate (0.8 mM) was added to determine FVIIa amidolytic activity. Data were presented in percentage of activity compared with WT FVII.