Prothrombin activation in the presence or absence of PCPS. The initial velocity of thrombin generation was determined at increasing concentrations of prothrombin in the presence (A) or absence (B) of 50 μM PCPS and 3 μM DAPA with 0.1 nM pt-FXa and 20 nM hFV-810 (⧫ or ◊), pt-rFV (● or ○), pt-rFV-QQ (▲ or △), or pt-rFVa (■ or □). The lines were drawn after analysis of all datasets to a rectangular hyperbola, and the fitted kinetic constants can be found in Table 1. The data are representative of 2 similar experiments.