Simulated liposomal flux assay. Simulations are conducted as virtual liposomal flux assays. The simulation begins with a 10-fold proton gradient and identical drug concentration inside and outside the proteoliposome. We assume infinite buffering capacity, so the proton gradient, represented as H_r, remains constant throughout the simulation. Unless otherwise indicated, H_r is set at 10. The simulation is then run until the drug concentration reaches steady state. Transport outcome is assessed by T_r, or the ratio of internal to external drug concentration at steady state (T_r = [Drug]_int/[Drug]_ext).