Binding of sDI to DII/DIII-uPAR mediated by the scuPA linker mutants. Binding of ¹²⁵I-sDI (50 nM) to 293 cells expressing GPI-DII-DIII of uPAR was measured in the presence of the indicated (0 to 400 nM) concentrations of WT-scuPA (▪), scuPA-43-49Ala (▵), ΔLeu43-45-scuPA (□), scuPA-Lys48Pro (⋄), or scuPA-Ser47Gly (•). Binding was measured as described in the legend to Figure 7. The data shown are from a single experiment representative of 2 so performed.