Fig. 4.

Effect of the number of estimated parameters on the parameter robustness and accuracy of the fit. When four parameters are estimated (K_b, K_t, K₁ and K₂) by different parameter methods, the parameter values vary in a wide range, while the differences in the accuracy of the fits are minor (Fig. 3). (A) The reduction of the number of parameters from four to two by fixing K₁ to 0.25 μM⁻¹ and K_t to 170 displays some minor differences in quality of the fits, but minimizes the difference of the values of the estimated parameters by the different methods (Table 1); (B) the reduction of the number of parameters from four to three by fixing K₁ to 0.25 μM⁻¹ and then to two by fixing K_t to 170 showed minor differences in quality of fit obtained by the DSL method. Despite these differences, the reduction in the number of parameters minimizes the difference in the values of the estimated parameters by the different methods, but at the expense of the accuracy of the fits. Shown are the fits of the stopped-flow transients at pCa= 8.9 for excess actin concentration to S1. The concentrations of actin and S1 are the same as in Fig. 3 and the backward rate constants are denoted in Fig. 1; the other equilibrium constants and error are shown in Table 1.