Figure 7.
The pH profile and apparent affinity of MdtM for Na+ and K+. (A) The pH profile of MdtM-mediated Na+/H+ and K+/H+ antiport activity. Transporter activity at each pH value was calculated as described in Methods. (B) The concentration of Na+ and (C) K+ required for the half-maximal acridine orange fluorescence dequenching response was estimated from measurements of the antiport activity of wild-type recombinant MdtM as a function of cation concentration at the previously determined pH optimum for each antiport reaction (pH 9.25 for Na+/H+ exchange and pH 9.0 for K+/H+ exchange). The [Na+]1/2 and [K+]1/2 values are an indication of the affinity of MdtM for each cation. In each panel, the data represent the mean ± SD of three independent experiments.