Competition of factor IXa binding to immobilized LMWH by soluble DHG and LMWH. Increasing concentrations of DHG (•) or LMWH (○) were preincubated with 100 nM factor IXa for 10 minutes prior to injection over reference and immobilized LMWH surfaces on the BiaCore 2000. Injections were performed and sensograms generated as described in “Materials and methods.” The concentration of free factor IXa was determined by the binding response at 90 seconds after injection. The concentration of glycosaminoglycan was plotted versus the proportion of remaining free factor IXa and fit by nonlinear regression to obtain the EC₅₀ for competition by the glycosaminoglycan (see “Materials and methods”). The fitted values for the EC₅₀ ± SE were 0.011 ± 0.002 μM for DHG and 0.38 ± 0.05 μM for LMWH.