KdpD-C and C499-894 have inactivation kinetics like KdpD. (A) HAK006 cells expressing KdpD, KdpD-C, or C499-894 were grown to mid-logarithmic phase in minimal medium containing 0.1 mM KCl. Samples were taken at the indicated time points after addition of 6 mM KCl and assayed for β-galactosidase activity. (B) HAK006 cells expressing KdpD, KdpD-C, or C499-894 were grown to mid-logarithmic phase in minimal medium containing 0.1 mM KCl and divided into aliquots. The indicated amounts of KCl were added to the cultures, and growth was continued for 6 h. The β-galactosidase activity was determined and normalized to the value of the initial culture for each sample.