FIGURE 7.

System response to a change in [Ca²⁺]. (a) Ca²⁺ titration, mean FRET distance versus pCa (−log([Ca²⁺])). Empirical fit to the Hill equation (green) (n = 1.18; pCa₅₀ = 5.82). Global fit to the model (Eqs. 2, 5, and 6) (red) (βΔμ′ = 22.9 kJ/mol). (b) The experiment-resolved macroscopic free energy landscape (see text, T = 15 C). Ca²⁺-unbound system-states (green). Ca²⁺-bound system-states (blue). Population density (spheres, radius represents magnitude) at the extremes of activation. pCa₅₀ (labeled as a right arrowhead).