FIG 3.

Antiport activity as a function of the cation concentration and pH. (A and B) Fluorescence-based assays of the Na⁺/H⁺ antiport activities of MrpA in E. coli strain mrpA EP432 vesicles were conducted at pH 8.0 over a range of concentrations of added NaCl (A) and LiCl (B). (C) Effect of pH on Na⁺/H⁺ antiporter activity of MrpA in vesicles of E. coli strain EP432 (□) and E. coli strain mrpA EP432 (■). The assay mixtures contained 100 mM NaCl. The error bars indicate standard deviations of the results of three independent assays.