FIGURE 3.

GadC-ΔC exhibits pH-dependent transport of Glu and Gln. A, the transport of Glu was robust at pH 5.5 and rapidly decreased with increasing pH values, with no detectable transport activity at pH 7.0 and above. The transport of Glu by the C-plug-deleted GadC variant (GadC-ΔC) was measured in a proteoliposome-based assay at different pH values. In this assay, the proteoliposomes were loaded with 5 mm Glu, and the external buffer contained 50 μm unlabeled Glu and 0.2 μm [³H]Glu. B, the transport of Gln was still measurable at pH 8.0. The transport of Gln by GadC-ΔC decreased with increasing pH values, but the rate of decrease was markedly slower than that for transport of Glu.