Figure 3. Ca²⁺/H⁺ exchange activity of PfCAX.

ΔpH-dependent uptake of 10 µM ⁴⁵Ca²⁺ into vacuolar-enriched membrane vesicles isolated from K665 (pmc1 vcx1) yeast transformed with empty vector (piHGpd) (A), scrcax1 (B), pfcax (C), and spfcax (D), measured over a 22 min time course. Transport measurements were determined in the presence of 0.1 mM NaN₃, 10 mM KCl, 1 mM ATP, 1 mM MgSO₄ and 0.2 mM orthovanadate (a Ca²⁺-ATPase inhibitor). ⁴⁵Ca²⁺ uptake in the absence (open symbols) or presence (closed symbols) of 5 µM of the protonophore CCCP is shown. The Ca²⁺ ionophore A23187 was added at 12 min at a concentration of 5 µM to dissipate any vesicle-loaded ⁴⁵Ca²⁺, as indicated by arrows. Points represent the mean ± SEM of 4–5 independent experiments (where not shown errors lie within the symbols).