Figure 3.

Effect of the addition of various concentrations of K⁺ (or Rb⁺) and (CH₃)₄N⁺ on the activities of WT-RMPK (A), E117K (B), T113L/E117K (C) and T113L/K114Q/E117K (D) mutants. Ionic strength and activities with 90 mM K⁺ (A) and without monovalent cations (B–D) were those indicated in the legend of Figure 2. The normalized control activities were shown in white columns in (A–D). White striped columns were in the presence of 25, 50, 75, and 100 mM (CH₃)₄N⁺ concentrations without K⁺ (or Rb⁺). In addition to the indicated (CH₃)₄N⁺ concentration, light gray, gray, dark gray, and black striped columns were in the presence of the 25, 50, 75, and 100 mM K⁺ (or Rb⁺) concentrations, respectively. The highest activities of RMPK mutants were achieved with ionic strength of 250 mM pointed out with *. Standard deviation bars of three experiments are shown.