FIGURE 3.

Substrate identity determines the transport rate in E. coli. In this competitive transport assay in E. coli, Eth⁺ efflux is monitored upon induction of (A) empty vector or (B) EmrE in BL21(DE3) with addition of external Eth⁺ (orange) or the competing ligands MeTPP⁺ (red), EtTPP⁺ (magenta), TPP⁺ (black), MBTPP⁺ (green), and DPhTPP⁺ (blue). The data shown are from a single batch of cells, to ensure equal protein expression levels between traces. Results were reproducible between batches of cells and were qualitatively similar between two BL21 cell lines. In A, the Eth⁺ trace from cells overexpressing EmrE was re-plotted as a dashed orange line for reference. Addition of CCCP inhibits Eth⁺ efflux (A, +CCCP).