Figure 3. TgNPT1 is an arginine transporter.

(a) [¹⁴C]Arg uptake into X. laevis oocytes expressing TgNPT1-HA (black), or into uninjected controls (grey). The data are derived from the 30 min time point of Supplementary Fig. 5b. Uptake was measured in the presence of 100 μM unlabelled arginine and 289 nM [¹⁴C]Arg. The data are averaged from three independent experiments and are shown±s.e.m. (**P<0.01; Student's t test). (b) [¹⁴C]Arg uptake, measured over 30 min, into X. laevis oocytes expressing TgNPT1-HA (black) or into uninjected oocytes (grey), in the absence (control) or presence of a 1 mM concentration of a range of unlabelled amino acids, and 289 nM [¹⁴C]Arg. The data are averaged from three experiments, each conducted on oocytes from a different frog, and are shown±s.e.m. (****P<0.0001; n.s.=not significant; ANOVA. Where P is not indicated for comparisons between uptake in the presence and absence of unlabelled amino acids in TgNPT1-HA expressing oocytes, the differences are not significant). (c) Concentration-dependence of TgNPT1-mediated arginine transport in X. laevis oocytes expressing TgNPT1-HA. [¹⁴C]Arg uptake was measured over 30 min in the presence of varying concentrations of arginine (0–1 mM). At each of the arginine concentrations tested, uptake measured in uninjected oocytes was subtracted from that in oocytes expressing TgNPT1-HA to yield TgNPT1-mediated transport. The data were averaged from three experiments, each conducted on oocytes from a different frog, and are shown±s.e.m. The Michaelis–Menten equation was fitted to the data by non-linear regression (K_m=88±16 μM, mean±s.e.m.; V_max=3.5±0.1 pmol oocyte⁻¹ min⁻¹, mean±s.e.m.).