FIGURE 4.

Antiport activities of antiporters in sub-bacterial vesicles. Fluorescence-based assays were monitored in a buffer containing 10 mm Tris-MES (pH 8.0), 140 mm choline chloride, 5 mm MgCl₂, 1 μm acridine orange, and 60 μg of vesicle protein were used in the assay. At the onset of the experiment, 5 mm Tris-l-lactate was added, and the resulting fluorescence quenching was recorded. The antiporter activity was measured from the dequenching of fluorescence upon the subsequent addition of 10 mm Na⁺, K⁺, or Li⁺. KNabc/pEASY carrying the empty vector was used as negative control, and KNabc/nhaA harboring Ec-NhaA was used as positive control. AU, arbitrary units.