Figure 1.
Figure 1. The D112V mutation abolishes current, but V116D restores proton-specific current, an example of second-site suppression. Whole-cell currents at pHo 7.0 and pHi 5.5 during pulses in 10-mV increments up to the indicated voltages for WT (A), D112V (B), or D112V/V116D (C), all expressed in COS-7 cells. Holding potential (Vhold) and pulse durations were −90 mV, 1 s (A), −40 mV, 3 s (B), and −60 mV, 2 s (C). In all cases, the voltage was returned to Vhold after the pulse, which is why the tail currents are inward for A and outward for C. Cartoons in all figures indicate S1 and S4 helices, with color coding as follows: red, Asp or Glu; yellow, Val; blue, Arg; gray, other amino acids or nonpore-facing residues.

The D112V mutation abolishes current, but V116D restores proton-specific current, an example of second-site suppression. Whole-cell currents at pHo 7.0 and pHi 5.5 during pulses in 10-mV increments up to the indicated voltages for WT (A), D112V (B), or D112V/V116D (C), all expressed in COS-7 cells. Holding potential (Vhold) and pulse durations were −90 mV, 1 s (A), −40 mV, 3 s (B), and −60 mV, 2 s (C). In all cases, the voltage was returned to Vhold after the pulse, which is why the tail currents are inward for A and outward for C. Cartoons in all figures indicate S1 and S4 helices, with color coding as follows: red, Asp or Glu; yellow, Val; blue, Arg; gray, other amino acids or nonpore-facing residues.

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