Figure 2.

Initial rates of the intermembrane transport of fluorescent phospholipids as a function of ΔpH. The magnitude of ΔpH across the membrane was adjusted by a 200-fold dilution of the donor vesicles (internal pH, 7.0) into buffers of different pH values. All reaction mixtures contained 5 mM MgCl₂. AcrA, when added, was at 25 μg/ml. (Inset) Time course of NBD fluorescence dequenching by AcrB-containing vesicles in the presence of AcrA, which was present at 90 (top curve), 60, 30, 15, or 0 μg/ml (bottom curve). Intravesicular pH was 7.0, and the pH of the assay buffer was 6.0. MgCl₂ was present at 5 mM.