Effect of 3-Cl-DPA on the rate of Ca²⁺ dissociation from the regulatory N-domain of intact cTnC. (A) Plot of the apparent rates of Ca²⁺ dissociation from the N-domain of intact cTnC in the presence of increased concentrations of 3-Cl-DPA or TFP. Each data point represents an average of at least three measurements ± SEM. (B) Representative stopped-flow traces as Ca²⁺ is removed from the N-domain of intact cTnC in the absence or presence of 100 µM 3-Cl-DPA or TFP. The traces have been normalized and staggered for clarity. Rates of Ca²⁺ dissociation were measured following fluorescence of IAANS attached to Cys⁵³ of cTnC with C35S, T53C, and C84S substitutions.