ΔYY and ΔKESYY truncations shift ouabain-sensitive transient charge movements to more negative potentials and accelerate charge relaxation at positive potentials. (A and B) Charge–voltage distributions determined from OFF voltage steps (as for closed symbols in Fig. 8 [D and H]) were normalized by their estimated amplitude from fits (Q_max–Q_min, 12.1 nC and 5.4 nC, respectively, for Fig. 8 [D and H]) and were averaged. V_0.5 and z_q values for each pump type averaged as follows: WT (black), −16 ± 1 mV and 0.93 ± 0.03, n = 3; C113Y (red), −26 ± 1 mV and 0.70 ± 0.01, n = 13; RD (green), −44 ± 1 mV and 0.74 ± 0.02, n = 12; C113Y-ΔKESYY (blue), −96 ± 2 mV and 0.62 ± 0.05, n = 7; C113Y-ΔYY (olive), −75 ± 1 mV and 0.67 ± 0.01, n = 5; RD-ΔKESYY (magenta), −114 ± 2 mV and 0.59 ± 0.02, n = 11; RD-ΔYY (orange), −95 ± 2 mV and 0.60 ± 0.02, n = 5. (C and D) Single exponential fits to the decay time courses of the transient current elicited by the ON voltage steps (e.g., Fig. 8 C, red lines) gave relaxation rates of the slow components of charge movement; their mean values are plotted against voltage in C and D. Error bars represent SEM.