FIGURE 6. Effect of Na⁺ on [5F]Hir-(54 – 65)( ${\text{SO}}_3^{-}$) binding to FPR-MzT and FPR-MzT(−F1).

Titrations of the change in fluorescence (ΔF/F_o) of 20 nM [5F]Hir-(54 – 65)( ${\text{SO}}_3^{-}$) in buffers containing NaCl (closed symbols) or ChCl (open symbols) as a function of the total concentrations of FPR-MzT (● and ○) and FPR-MzT(−F1) (▲ and △) ([FPR-MzT or FPR-MzT(−F1)]_o). The solid lines represent the nonlinear least-squares fits of the titrations by the quadratic binding equation with the parameters listed in Table 1. Titrations were performed and analyzed as described under “Experimental Procedures.”