FIG. 2.

H⁺-norfloxacin antiport via AbeM. H⁺-norfloxacin antiport was measured in everted membrane vesicles prepared from cells of E. coli KAM32/pUC18 (control) (curve a) and E. coli KAM32/pABE618 (carrying abeM) (curve b). The formation and dissipation of the H⁺ gradient across vesicle membrane, which reflect the influx and the efflux of H⁺, respectively, were monitored by measuring the changes in fluorescence intensity of quinacrine. At the time points indicated by arrows, potassium d,l-lactate (final concentration, 5 mM) was added to initiate respiration. After the fluorescence quenching reached a steady-state level, norfloxacin (final concentration, 5 μM) was added to the assay mixture, and then CCCP (final 50 μM) was added to collapse the H⁺ gradient.