Figure 4. Dependence of active ethidium efflux on the composition of the proton-motive force (Δp).

Ethidium transport was measured as described in the legend to Fig. 3A for cells without LmrP (control) or with Wt LmrP, or expressing mutant K357A (panel A) or R260A (panel B). Composition of Δp (interior negative and alkaline) in cells in KPi buffer was manipulated by the addition of 1 µM of the ionophores nigericin (+N) or valinomycin (+V) that dissipate the ΔpH and Δψ, respectively. Traces represent observations in at least four independent experiments (n = 4).