FIGURE 1. Effect of Na⁺ on [5F]Hir-(54 – 65)( ${\text{SO}}_3^{-}$) binding to ProT zymo-gen forms.

Changes in fluorescence (Δ F/F_o) of 50 nM [5F]Hir-(54 – 65)( ${\text{SO}}_3^{-}$) as a function of the total concentrations of ProT ([ProT]_o) (A), Pre 1 ([Pre 1]_o) (B), and Pre 2 ([Pre 2]_o) (C) are shown for experiments in buffers containing NaCl (●) or ChCl (○). The solid lines represent the nonlinear least-squares fits by the quadratic binding equation with the parameters listed in Table 1. Titrations were performed and analyzed as described under “Experimental Procedures.”