H+/Ca2+exchange driven by the plasma membrane Ca2+‐ATPase of Arabidopsis thalianareconstituted in proteoliposomes after calmodulin‐affinity purification

The plasma membrane Ca2+‐ATPase was purified from Arabidopsis thalianacultured cells by calmodulin (CaM)‐affinity chromatography and reconstituted in proteoliposomes by the freeze‐thaw sonication procedure. The reconstituted enzyme catalyzed CaM‐stimulated 45Ca2+accumulation and H+ejection, monitored by the increase of fluorescence of the pH probe pyranine entrapped in the liposomal lumen during reconstitution. Proton ejection was immediately reversed by the protonophore FCCP, indicating that it is not electrically coupled to Ca2+uptake, but it is a primary event linked to Ca2+uptake in the form of countertransport.