Rate constants for the C_i-O_i transitions in Scheme 1* (Fig. 6 D) determined from fits to WT τ_K-V relations in 0-100 mM Mg²⁺ (Fig. 7 A), using equilibrium parameters from Table I (WT, WT_B). Since voltage sensor activation equilibrates rapidly, τ_K was fit by

⁠, where i represents the number of activated voltage sensors, δ_i and γ_i are forward and backward rate constants for the C_i-O_i transitions and pC_i, pO_i are conditional occupancies of the open and closed states (pC_i = p(C_i|C), pO_i = p(O_i|O)) (Horrigan et al., 1999). Forward rates (δ_i) were varied while backward rates were γ_i = δ_i/L₀Dⁱ and partial charges associated with these rate constants were z_δ = 0.165e and z_γ = −0.135e (Horrigan and Aldrich, 2002).