FIGURE 6. Adenine transport and metabolism in Xenopus oocytes.

(A) Adenine metabolism in oocytes expressing PfENT4, PvENT4 or injected with H₂O. Oocytes were incubated for 60 min in 150 nM [³H]adenine. The metabolic fate of the imported adenine was analyzed by HPLC. Fractions were collected and analyzed for the presence of radioactivity. The retention times for adenine, adenosine, adenosine 5′-mono- (AMP), di- (ADP) and tri-phosphate (ATP) are indicated. (B, C) Competition of increasing concentrations of unlabeled adenine on the uptake of 150 nM [³H]adenosine (B) or 1.5 μM [¹⁴C]2′-deoxyadenosine (C) into oocytes expressing PfENT4 (black circles) or PvENT4 (gray triangles). Competition data was background-subtracted and normalized to a % of uptake in the absence of unlabeled competitor. In panel (B) each point represents the average from two separate experiments, one experiment in which individual oocytes were solubilized and counted and the other in which 8 oocytes were pooled together and counted as one sample. In panel (C), each point represents the normalized mean uptake of 15 oocytes derived from 3 separate experiments. Data are fit with a single site competition curve.