Figure 5. Chloramphenicol/proton antiport in proteoliposomes.

(a,b) Effect of the ΔpH on the uptake of 2 μM of the neutral antibiotic [³H]-chloramphenicol (CM) over time (a) and at 5 min (b) in proteoliposomes containing MsbA-WT or MsbA-MD, or in liposomes without MsbA proteins. (c) CM uptake by in proteoliposomes is associated with H⁺ efflux through drug/proton antiport. The CM-dependent increase in fluorescence emission of the trapped pH probe BCECF in MsbA-WT-containing proteoliposomes but not in empty control liposomes indicates an increase in the lumen pH during the MsbA-WT catalysed reaction. Histogram shows BCECF fluorescence levels at 550 s. The error bars for some of the data points in (a) were too small to be displayed, and are hidden behind the data point symbols. Data represent observations in three or more independent experiments with independently prepared batches of proteoliposomes. Values in histograms are expressed as mean±s.e.m. (one-way analysis of variance ; ***P<0.001; ****P<0.0001).