Figure 2.

Internal substrate dependence on the transport activities of GsTPT, GsPPT, and GsGPT. A to C, Liposomes were preloaded with various substrates (30 mm) and reconstituted with membrane proteins from yeast cells expressing GsTPT (A), GsPPT (B), or GsGPT (C). Uptake experiments were initiated with 0.25 mm [³²P]Pi (A and B) or 1 mm [³²P]Pi (C) and terminated after 1.5 min (GsTPT), 2 min (GsPPT), or 4 min (GsGPT). As negative control, proteoliposomes were preincubated (2 min) with inhibitor stop solution to calculate net uptake activity. Relative uptake activities were compared to the Pi/Pi counter-exchange experiment, which was set to 100%. Data are summarized as the arithmetic mean ± se of at least three independent experiments. Glc6P, Glc-6-P; Glc1P, Glc-1-P; Frc6P, Fru-6-P; Gal1P, Gal-1-P; Gly3P, Gly-3-P.