Figure 6.
Competitive binding titrations of SC(1–246) N-terminal double mutants that bind weakly to ProTQQQ. Titrations of the probe, SC(1–246)-BODIPY (29 nm (○) and 502 nm (●)) with ProTQQQ from Fig. 4 served as reference curves for competitive titrations of SC(1–246) mutants. The probe concentration for all of the competitive titrations (▴) in A–F was 50 nm. Concentrations of competing SC(1–246) mutants were as follows: G1G2 8.12 μm (A), R1R2 9.06 μm (B), K1A2 9.50 μm (C), E1T2 9.04 μm (D), R1Q2 10.30 μm (E), and E1S2 11.38 μm (F). Titrations of probe and competitor were simultaneously analyzed by the cubic binding equation to obtain KC, stoichiometry, and maximum fluorescence intensity (ΔFmax/Fo) of the SC(1–246) mutants (Tables 2 and 3).