FIG. 4.

Electrogenicity of Mrp-dependent Na⁺/H⁺ antiport. Fluorescence-based assays of everted membrane vesicles from the control, Mrp_BpOF4, and Mnh transformants of E. coli EP432 were performed in reaction mixtures containing 200 μg vesicle protein/ml in a total of 2 ml. The reaction mixtures contained 50 mM BTP-sulfate, 5 mM MgSO₄, 200 mM K₂SO₄, and 1 μM nigericin at pH 7.5, plus 1 μM oxonol VI. To initiate respiration, 1 mM Tris-NADH was added at the first arrow. Once the quenching achieved steady state, 10 mM NaCl was added at the second arrow. The final arrow indicates the addition of 10 μM carbonyl cyanide m-chlorophenylhydrazone (CCCP). The traces shown are representative of at least three independent experiments.