VEGF Conversion to VEGFf Impacts Binding to VEGFR1 and VEGFR2. Simulations were run for 2 h using baseline parameter values. The total concentration of VEGF and VEGFf was kept constant at 0.45 nM and VEGFR1, VEGFR2, and NP-1 equal at 12,000 #/cell. (A) VEGF bound to VEGFR2 or VEGFR1 for Model 1 (VEGFf can bind to VEGFR1 alone or when VEGFR1 is bound to NP-1 -open) and Model 2 (VEGFf cannot bind to VEGFR1 bound to NP-1 - filled) are shown. (B) VEGFR1 binding by VEGFf (Model 1- open circle, Model 2 -filled circle), or the sum of both VEGF and VEGFf bound to VEGFR1 (Model 1 - open square, Model 2 -filled triangle) is plotted. (C). NP-1 complexes increase for Model 1. VEGF-VEGFR2-NP-1 complexes (Model 1-open square), VEGF-VEGFR1-NP-1 (Model 1 - open triangle), and the sum of VEGF-VEGFR1-NP-1 and VEGF-VEGFR2-NP-1 complexes (Model 1 -open circle, Model 2 - filled circle). Note that there are no VEGF-VEGFR1-NP-1 complexes with Model 2.