Fig. 3

Heterologously expressed SLC35B1 and SLC35B1/Isoform 2 are antiporters for ADP and ATP. a, b After 5 min of uptake of 20 µM [α³²P]ATP as described in Fig. 2, efflux was induced by the addition of ten-fold molar excess of unlabeled ATP. Data are reported as the mean of at least three independent experiments and are shown with the standard error of the mean (SEM). See Supplementary Fig. 2 for the demonstration of ATP export into the cell supernatants under similar conditions. c–f Proteoliposomes harboring membrane proteins from SLC35B1 (c, d) or SLC35B1/Isoform 2 (e, f) transfected E. coli cells were prepared as described in Methods. Time dependent accumulation of 50 µM [α³²P]-ATP in unloaded (pink) or preloaded proteoliposomes (c, e) or 50 µM [α³²P]-ADP in unloaded (light green) or preloaded proteoliposomes (d, f). Proteoliposomes were preloaded with 10 mM ADP (empty rhombs) or 10 mM ATP (filled rhombs). [α³²P]-ATP or [α³²P]-ADP was present at a concentration of 50 µM. Uptake was terminated after 2 min. Data are reported as the mean of at least three independent experiments and are shown with the standard error of the mean (SEM)