Simulations of the pH-dependent uptake of Arg ⁺ under asymmetric conditions using our model in two configurations of opposite sidedness. (A and B) Fractional uptake values (mean ± SEM) were previously reported by Tsai et al. (2012), which were obtained via assaying radioactive Arg⁺ fluxes into vesicles with AdiC reconstituted in the outside-out or inside-out orientation (closed blue bars). As initial conditions, the solution of pH 5 in vesicles contained 5 mM Arg⁺, whereas the bathing solution of pH 3 or pH 5 contained 50 μM of radioactive Arg⁺. The fractional uptake values were determined 5 min after the initiation of the experiments. We simulated their data using our model in the configurations 1 (A) and 2 (B) of opposite sidedness illustrated in Figs. S6 and S7, respectively (closed oranges bars; mean ± σ). The kinetic parameters for the two different sides of the model were those determined in the corresponding pH conditions. (C and D) The ratios between the experimental values for pH 3 and pH 5 in the outside or inside-out orientation (open blue bars) compared with those predicted by the model in configuration 1 (C) and 2 (D) (open orange bars).