Influence of FXa on thrombin generation in hemophilic plasma. Thrombin generation was measured for 90 minutes at 37°C in HA plasma supplemented with increasing concentrations (dark red, 0.003; magenta, 0.01; blue, 0.03; green, 0.1; orange, 0.3; and red, 1.0nM) of wt-FXa (A) or FXa^I16L (B) in the presence of 2.0pM TF/4μM phospholipid (reagent RB; Technoclone). Thrombin generation was initiated with CaCl₂ and a thrombin fluorogenic substrate as detailed in “Methods.” For panel A, the black squares are a representative run of NHP, and for panel B the black circles represent a typical run of HA plasma (essentially undetectable). The endogenous thrombin potential (ETP; C) for each protease is plotted as a function of the protease concentration (wt-FXa (■); FXa^I16L (●), rFXa^V17A (▴), and rFVIIa (♦). In panel C, the dashed line represents the average ETP obtained for NHP. In each of the panels, the lines are arbitrarily drawn. The data are representative of 3 similar experiments.