FIGURE 2. Effect of Na⁺ on [5F]Hir-(54 – 65)( ${\text{SO}}_3^{-}$) binding to thrombin and FPR-thrombin.

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