Vacuolar cation/proton exchanger (CAX). Translocates Ca(2+) and other metal ions into vacuoles using the proton gradient formed by H(+)-ATPase and H(+)-pyrophosphatase. Cation selectivity transport in tobacco root tonoplast vesicles is Cd(2+)>Zn(2+)>>Ca(2+)>>>Mn(2+). Tonoplast. Expressed at low levels in all tissues. Slightly induced by Mn(2+), Na(+) and Ni(2+). CAX4 expression in tomato increases calcium content and prolonges shelf life and may serve as an alternative to the application of CaCl(2) used to extend shelf life in numerous agricultural commodities. Belongs to the Ca(2+):cation antiporter (CaCA) (TC 2.A.19) family. Cation/proton exchanger (CAX) subfamily.