Fig. 7.

The effective kinetic binding rate constant, kobs (in s⁻¹), shows sigmoidal dependence on pCa. For all three-parameter estimation methods kobs is calculated using Eq. (6) (McKillop and Geeves, 1993) and the values of K_b and K_t are shown in Fig. 6. (A) k_obs shows minor differences between different parameter estimation methods regardless of large fluctuations in values K_b and K_b and agrees well with the k_obs obtained from single exponential fits of experimental data (Boussouf et al., 2007a) for lower Ca²⁺ concentrations. (B) Estimated fractional equivalent rate constant $k_{\mathit{\text{obs}}}^f$ by any of the three-parameter estimation methods agrees well with $k_{\mathit{\text{obs}}}^f$ derived from the single exponential fits to the experimental data after appropriate normalization. However, the Hill coefficient for the estimated values somewhat overestimates the Hill coefficient derived from the exponential fits (i.e. 2.6 vs. 1.79, respectively) reflecting some methodological differences in assessing k_obs (or $k_{\mathit{\text{obs}}}^f$) from estimated rate constants vs. directly from experimental data.