TABLE 2.

Equilibrium binding constants for prothrombinase assembly

The errors in the fitted constants represent ± 2 S.D. Data are representative of two to three similar experiments.

Competitor speciesa	Kd, compb	Kd, fixedc
	nm
rFXaS195A	1.34 ± 0.17	1.04 ± 0.17
rFXaI16L	13.8 ± 1.07	1.22 ± 0.07
rFXaV17A	7.25 ± 0.65	1.04 ± 0.23
Active site blockedd
EGR-rFXa	1.80 ± 0.42	1.05 ± 0.31
EGR-rFXaI16L	1.92 ± 0.20	1.05 ± 0.14

^aReaction mixtures containing 10 nm OG₄₈₈-FXa, 50 μm PCPS and either 8 or 10 nm FVa in assay buffer were titrated with increasing concentrations of the competitor species. Fluorescence intensity was recorded as described under “Experimental Procedures.” For simplicity, the primary data in Fig. 4 is shown with only one fixed concentration of FVa.

^bRepresents the equilibrium dissociation constant of the competitor species.

^cRepresents the equilibrium dissociation constant of the fixed species (i.e. OG₄₈₈-FXa).

^dWild-type rFXa and rFXa^I16L were covalently modified at the active site with EGR-CH₂Cl, as described under “Experimental Procedures.”