FIGURE 10.
Effect of APC(S360A) and FPR-APC on FX activation by the intrinsic tenase complex. FVIIIa (140 pm) was incubated with 40 μm phospholipid vesicles (10:90, DOPS:DOPC) and varying total concentrations of FPR-APC (●) or APC(S360A) (○) in Buffer II for 15 min. FIXa (1 nm) was added, and after 15 s, FX activation was started by the addition of 400 nm FX. Samples from the reaction mixture were taken at 5 and 8 min, diluted in EDTA buffer, and assayed for FXa with the chromogenic substrate S-2765. Initial rates of FX activation were expressed as percentages of the rate of FX activation determined in the absence of APC (vobs/vo). The experiments were performed as described under “Experimental Procedures.” The average initial rate of FXa formation ± S.E. from two different experiments is plotted as a function of the total concentration of APC(S360A) ([APC(S360A)]o or FPR-APC [FPR-APC]o).