FIGURE 10.

Kinetic parameters of K⁺ uptake by cells containing KtrB variants with single or double amino acid changes in the putative salt bridge residues Asp²²² and Lys³²⁵. Plasmid-containing cells of strain LB2003 were grown and induced for ktrB expression with 0.02% l-arabinose as described under “Experimental Procedures.” For the K⁺ uptake experiment, K⁺-depleted cells were suspended at 1 mg dry weight/ml of medium containing 200 mm NaHepes, pH 7.5, 0.2% glycerol, and 0.02% l-arabinose. The suspension was shaken at room temperature. After 10 min, KCl was added at following concentrations: 0.5, 1, 2, and 5 mm. For each data point, a 1.0-ml sample was taken from the suspension, and its cell K⁺ content was determined by flame photometry. V_max (A) and K_m (B) were determined by the Eadie-Hofstee method. Error bars, S.D.