Comparison of Zn²⁺ inhibition of proton current in V116H, D185N, and WT hH_V1 and in the Zn²⁺-insensitive H140A/H193A background. Inhibition of H⁺ current by Zn²⁺ at +60 mV in the V116H/H140A/H193A mutant (●), WT hH_V1 (▪), V116H/H140A/D185N/H193A (♦), and background construct H140A/H193A (▴). The mean ± SEM ratio of test pulse current in the presence of Zn²⁺ to its absence is plotted. Solid symbols and lines show measurements at pH_o 7, open symbols and dashed lines at pH_o 6. For concentrations <1 µM, Zn²⁺ was buffered with ADA. Numbers of cells, from low to high [Zn²⁺], for V116H are 6, 3, and 6 at pH_o 7; 3, 3, and 8 at pH_o 6; for WT 13, 10 and 7 at pH_o 7; 4, 6, 5, 4, and 1 at pH_o 6; for V116H/D185N 3, 4, and 4 at pH_o 7; 4, 4, 4, and 3 at pH_o 6; and for H140A/H193A 2, 5, 6, 4, and 1 at pH_o 7; 3, 3, 3, 3, and 3 at pH_o 6.