Activation of PC and thrombin-activatable fibrinolysis inhibitor (TAFI) by thrombin and cells expressing TM-WT or the TM-C265S mutant. (A) Cells expressing WT or C265S mutant TM were incubated with PC and thrombin at 37°C for 30 minutes before stopping the reaction by the addition of antithrombin and heparin. The amidolytic activity of activated PC was assayed using S-2366 (n = 3 experiments; mean ± SD). Nontransfected cells showed no detectable activity. (B) Cells expressing WT or C265S mutant TM were incubated with TAFI and thrombin at 37°C for 10 minutes before stopping the reaction by the addition of d-phenylalanyl-prolyl-arginyl chloromethyl ketone. The carboxypeptidase activity of activated TAFI was assayed using hippuryl-l-arginine (n = 3 experiments; mean ± SD). Nontransfected cells showed no detectable activity.