Fig. 9.

Experimental imperfections and quality of the fit. Estimated parameters at pCa = 5.2 shown in Figs. 6 and 7 significantly differ from the values estimated at neighboring Ca concentrations, as well as those estimated by different parameter estimation methods at pCa = 5.2. Parameter values for K_B and K_T vary in wide range (K_b = 11.22, 15.79 and 29.81, K_T = 0.0988, 0.0848 and 0.0870, for DSL, QN and SA, respectively), but all three fits differ a little and differences in errors are minimal (error=3.260 × 10⁻⁵, 3.327 × 10⁻⁵ and 3.318 × 10⁻⁵, respectively). Thus the main difference of the estimated parameters at pCa = 5.2 is rather in high sensitivity of estimated fits to minor perturbations in experimental data. In contrast, large deviation of the estimated values at pCa = 5.2 compared to neighboring concentrations is rather caused by imprecise determination of the timing of the beginning of the experiment or some other experimental imperfection (the beginning of any stopped-flow transient is always the most error-prone because of flow or stopping artefacts. Also, at the initial time points where signal changes can be large there can be an effect of the amplifier time constant if it is chosen to be optimal for the full transient). The reverse constants are denoted in Fig. 1 and the concentrations of actin and S1 are the same as in Fig. 3. Only K_B and K_T are estimated while K₁ and K₂ are kept constant at values of 0.25 μM⁻¹ and 170, respectively.