Figure 1.

Cation transport activity in proteoliposomes. AtNHX1 and LeNHX2 proteins were purified and reconstituted into liposomes to measure their cation/H⁺ exchange activity as described.¹¹,¹⁷ An acid-inside pH gradient was created by dilution of proteoliposomes containing (NH₄)₂SO₄ into ammonium-free assay buffer at pH 7.5. Fluorescence recovery, indicative of vesicle alkalinization, was measured upon addition of NaCl and/or KCl salts to the assay medium. Addition of 25 mM (NH₄)₂SO₄ disrupted the pH gradient and ended the assay. Transport activities are given as percent of maximal fluorescence. (A) Proton exchange rates of AtNHX1 were determined in the presence of 50 mM NaCl (green trace), 50 mM KCl (red trace), and 50 mM of each salt (black trace). (B) Transport activity of LeNHX2 with 125 mM NaCl, 125 mM KCl and 125 mM of each salt; trace colors as in (A).