Figure 3.

pH_I-dependence of the transition rates at 0 mV. The parameters α₀ and β₀ (Eqs. 1 and 2 ) were obtained from fitting proton currents to the four-state model. These coefficients are the rate constant of the reaction in the absence of any electrical field, thus they correspond to the chemical component of the reaction. All coefficient were sensitive to pH_I, where the forward rates increased as the intracellular side was acidified, whereas the backward rate increased when the intracellular side was alkalinized. The red lines correspond to the fit of the logarithm of the rates as a function of pH_I. The slope of this traces constitute a measure of pH_I-dependence of these rate coefficients, so that increasing the steepness of the slope indicates higher pH_I sensitivity (see Fig. 5). To see this figure in color, go online.