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. 2008 Apr 28;105(19):6900–6905. doi: 10.1073/pnas.0800873105

Fig. 2.

Fig. 2.

Mutations of select residues just below the bundle-crossing shift KcsA pH sensitivity. (A) Po vs. pH plots with fits to the Hill equation (lines). E71A, background channel (open black circles): nH = 4.4 ± 0.1, pH0.5 = 5.3 ± 0.007; E118Q/E120Q (filled black circles), nH = 4.4 ± 1.2, pH0.5 = 5.5 ± 0.005; E118A/E120A (filled red circles), nH = 5.8 ± 0.2, pH0.5 = 6.6 ± 0.004. The locations of E118 and E120 in the KcsA structure are highlighted in red (Inset). (B) Po vs. pH curves with Hill fits: background (dashed black line); H25R (filled blue circles), nH = 1.9 ± 0.1, pH0.5 = 5.3 ± 0.01; H25R/E118Q/E120Q (filled black circles), nH = 2.5 ± 0.5, pH0.5 = 6.3 ± 0.04; H25R/R117Q/R121Q/R122Q (filled gray circles), nH = 1.8 ± 0.4, pH0.5 = 6.0 ± 0.05; H25R/E118A/E120A (filled red circles). The red line through the H25R/E118A/E120A red symbols has no theoretical meaning. The location of H25 is highlighted in blue with E118 and E120 in red (Inset). Error bars in A and B are the standard error of the mean for three to seven experiments. Error values for nH and pH0.5 are standard error estimates from the fit.