Fig. 2. Membrane binding of LukF and HS. (A) Binding of LukF–TMR (A1) or HS–IC5 (A2). [F_b] or [H_b] were plotted against [F_o] or [H_o] at 6 × 10¹⁰ (filled circles) and at 6 × 10⁸ (filled triangles) HRBC/l. The red lines represent the fitting of data (Appendix 1). (B) Binding of both LukF–TMR and HS–IC5 to 6 × 10¹⁰ HRBC/l. At four values of [F_o] (B1) and [H_o] (B2), the relative [F_b] and [H_b] were measured in the presence of the other at different concentrations. The lines represent theoretical values of F_b (H_b), calculated based on the binding and association constants.