Plasmin cleaves HK independent of contact system activation in plasma. (A) Western blot of human plasma HK in a normal, PK-deficient, and FXII-deficient patient. Green = polyclonal antibody against the light chain of hHK. Cleavage products of HK (∼52 kDa) are shown after the addition of vehicle (saline +0.2% glycerol), kaolin (200 µg/mL), or plasmin (116 µg/mL) for 1 hour at 37°C. (B) Western blot of plasma HK in WT, PK^−/−, and FXII^−/− mice. Green = polyclonal antibody against the FXI- and PK-binding domain within the light chain of HK. Mouse plasma was treated with either plasmin (μg/mL) at indicated concentrations or kaolin 200 µg/mL (K) for 1 hour at 37°C.