FXI activation. (A) FXI-WT activation. FXI-WT (200 nM) was incubated at 37°C with vehicle, or 40 nM FXIIa, or 140 nM thrombin in the presence of 4 μM polyphosphate. At various times, samples were removed into reducing sample buffer, size-fractionated by SDS-PAGE, and stained with Coomassie blue (top row). Positions of standards for FXI, and the heavy chain (HC) and light chain (LC) of FXIa are shown on the right of each image and positions of molecular mass markers in kilodaltons are shown to the left of the images. The white arrows indicate bands for FXIIa or thrombin that appear because of the high enzyme to substrate ratios in these reactions. Stained gels underwent densitometry scanning to generate the curves in the bottom row. Values for each band were compared with those for FXI at 0 minutes, which was assigned a value of 100%. Curves show the disappearance of FXI (Δ) and the appearance of the heavy chain of FXIa (□). (B) FXI-PlatRSR activation. FXI-PlatRSR was activated as in panel A with vehicle or with 40 nM FXIIa or 140 nM thrombin in the presence of 4 μM polyphosphate. Time course experiments were run and analyzed as in panel A.