Effect of terminal voltage-independent steps on the free energy estimates. (A) Two six-state linear schemes of voltage-dependent activation of a channel. In both schemes, except for the final transition (in bold), all other steps are voltage dependent. Scheme II has one open state, whereas scheme II has two open states. The voltage dependence of each of the equilibrium parameters in schemes II and III is defined similar to those in scheme I (Fig. 3 A). For schemes II and III, z₅ = 0. (B) Results of the numerical simulations performed using scheme II. $K30$ = 10, z₂ = 1.5, z₃ = 1, and z₅ = 0. The remaining parameters were same as those in scheme I (Fig. 3 A). $K50$ was varied from 0.001 to 2,097.15. The relation between the free energy difference between the initial and final states, $ΔG−C$ (⁠$−RTln∏i=15Ki0$⁠), and the free energy change in the ensemble, Q_maxFV_m (closed symbols) and $−RTlnPOmax$ (open symbols), for different values of $K50.$ Adding Q_maxFV_m and the correction factor, $−RTlnPOmax,$ gives $ΔG−C$⁠, as depicted by the dashed line. (C) $POmax$ values calculated at different values of $K50$ for scheme II (A).