Effects of mutations in the 558-565 loop on FIXa-catalyzed activation of factor X in the presence of PSPCPE.

Factor Xa generation assays contained 5 nM FIXa, 10 μM PSPCPE vesicles, variable FVIIIa concentrations, and were initiated with 300 nM FX as described in “Materials and methods.” (A) Data points obtained for FVIII_WT (▪) and FVIII_Arg562Ala(▴). (B) Data generated for FVIII_Ser558Phe (○), FVIII_Val559Ala (♦), FVIII_Asp560Ala (∗), FVIII_Gln565Arg (●). The data were plotted and fitted using a single-site ligand binding model as described in “Materials and methods.”