PKal is activated by tPA in human plasma. (A) Concentration-response curves of tPA in human plasma. Purified human tPA (0-360 nM) was incubated in human plasma for 10 minutes at room temperature. Kallikrein-like activity was determined by measuring changes in fluorescence at 410 nm because of hydrolysis of D-Pro-Phe-Arg-7-Amino-4-Trifluoromethylcoumarin. Data are expressed as fluorescence intensity and represent mean ± SEM of 3 independent experiments. **P < .01 vs vehicle. Insert: Dose response of inhibition of kallikrein-like activity by BPCCB (0.1-3 μM; n = 3 independent experiments). (B) Effects of tPA on kallikrein-like activity in normal, plasminogen-, FXII-, or prekallikrein-deficient plasma. Data are expressed as ∆ fluorescence intensity per minute and represent mean ± SEM of 3 independent experiments. **P < .01; ***P < .001. (C) Time course of PKal production by FXIIa. Purified human PPK (0.4 μM) was incubated with 0.5 μM purified human tPA or 0.5 μM purified human plasmin or 0.5 μM purified human FXIIa for time course. Analysis of the incubation mixture by western blot demonstrates PPK cleavage by FXIIa. (D) Time course of FXIIa production by plasmin and PKal. Purified human FXII (0.37 μM) was incubated with 0.5 μM purified human tPA or 0.5 μM purified human plasmin or 0.5 μM purified human PKal for time course. Analysis of the incubation mixture by western blot demonstrates FXII cleavage by plasmin and PKal. (E) Time course of FXIIa activity. Data are expressed as fluorescence intensity and represent mean ± SEM of 3 independent experiments.