FIGURE 6. Cooperative Ca²⁺ binding to the C-domain of CaM.

Panel A illustrates the microscopic equilibrium Ca²⁺ binding reactions associated with transition of the C-domain of CaM from the 0-Ca²⁺ to 2-Ca²⁺ states. The table in panel A lists optimized equilibrium and kinetic microscopic Ca²⁺ binding constants derived as described under “Experimental Procedures.” Panel B shows the relationship between observed Ca²⁺ association rates at free Ca²⁺ in the range of 1 to 5 μM. The closed circles are experimental data derived as described in the legend to Fig. 5E and under “Experimental Procedures.” The open circles are derived from a simulation carried out using the model described under “Experimental Procedures” and the binding parameters shown in panel A.