Estimation of vascular Col4 available for binding FIX. Blood samples were taken 10 minutes after infusion of different doses (8, or more, mice per dose) of FIX_WT into CRM⁻ mice. The data were fit to FIXt-C (the quadratic equation for equilibrium) and were plotted as the total infused FIX (x-axis) vs measured plasma FIX (y-axis). The empirically determined FIX concentrations were determined by ELISA (Methods).The plotted line is the fit of the experimental data (FIXt-C), where C is the calculated complex. The error bars represent the standard deviation of the mean for 8 or more mice for each level of infused FIX. The 2 light red points in the figure represent data collected in our laboratory about 5 years ago, and is only included as in internal check. The table above the figure represents the statistics of the quadratic fit.