Fig. 2.
(A) The effect of varying pHout (initial pHin = 7.0) on the magnitude of the net inward flux of protons into M2PL. The inner pH at the start of each experiment was 7, and the rates are quoted as protons per M2 tetramer and sec, extrapolated to time = 0. Squares: K M2PLs with valinomycin (Fig. 1A); circles: K M2PLs without valinomycin (Fig. 1B); triangles: Na M2PLs (Fig. 1C). The smooth curves through the data were generated using a kinetic scheme based on a proton relay mechanism to fit a conducting pKa and maximal rate to the data (see SI Text). Other mechanisms such as a gated channel also provided a reasonable fit to the data. (B) Inhibition of the initial rate of proton conduction driven by a K+/valinomycin-induced potential (62 mV), as a function of amantadine concentration. The data were fit with a sigmoidal binding isotherm with Kdiss = 1.3 μM.