Figure 3.

Sugar binding to Q457C. The binding of sugar to Q457C can be studied from the effect of external sugar on the presteady–state charge movement. Sugar shifted the V_0.5 of the Q/V relation. (A) The effect of sugar on Q/V relations. Normalized Q/V curves at 0 and 5 mM αMDG. The V_0.5 of the Q/V curve at 5 mM αMDG shifted +14 mV. Fits to the data gave, in Na⁺: Q_max 13 ± 1 nC, z = 0.9 ± 0.1, V_0.5 = −34 ± 2 mV; in 5 mM αMDG: Q_max = 12 ± 1 nC, z = 0.9 ± 1, and V_0.5 = −20 ± 4 mV. (B) Dependence of the V_0.5 on external sugar concentration. The curve was drawn according to the equation: ΔV_0.5 = ΔV_max [αMDG]/(K_0.5 + [αMDG]) with ΔV_max = 33 ±5 mV and K_0.5 = 12 ± 6 mM.