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. Involved in ion homeostasis in association with CAX3. May play a role in cold-acclimation response. Activated by monothiol glutaredoxin GRXS14 and CXIP4. Inhibited by excess of Ca(2+) and Cd(2+), Na(+) and K(+), but not Mn(2+). Measured in vacuolar yeast membrane vesicles with a shorter CAX1 starting at Met-37. Optimum pH is 7.5 for cytosolic pH. Interacts with GRXS14 and CXIP4. Tonoplast. Expressed at low levels in leaves, stems and flowers. By cold in leaves. Highly induced by Ca(2+) and at low levels by Na(+) and Ni(2+). Plants exhibit a 50% reduction in tonoplast Ca(2+)/H(+) exchange activity, a 40% reduction in tonoplast V-type H(+)-translocating ATPase activity, a 36% increase in tonoplast Ca(2+)-ATPase activity and an increased expression of CAX3 and CAX4. These plants exhibit altered plant development, perturbed hormone sensitivities, altered auxin signaling response, lower sensitivity to other metal ions and increased freezing tolerance after cold acclimation. CAX1 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. Expression in potato tubers increases calcium content by 3-fold without the adverse effect of increasing other metal ion contents. May be due to intron retention. Belongs to the Ca(2+):cation antiporter (CaCA) (TC 2.A.19) family. Cation/proton exchanger (CAX) subfamily.