FIGURE 2.

Inhibition of FV variants by B-domain fragments. A, structures of FV, FV-810 and FVa, indicating the presence of the BR (blue) and AR (red). B, the BR peptide (0–8 μm) was titrated into reaction mixtures containing 1.4 μm prothrombin, 3 μm DAPA, 50 μm PCPS, and 0.1 nm rFVa (○) or FV-810 (●) in assay buffer at 25 °C. Reactions were initiated with 2 nm FXa, and prothrombin activation was measured as described under “Experimental Procedures.” C and D, specific clotting activity was measured in FV-deficient plasma supplemented with 0.25 nm FV-810 (C) or rFVa (D) and the indicated peptides at 5 μm. Ac-BR, the acetylated BR peptide.