Contributes to the transtonoplast (from cytosol to vacuole lumen) H(+)-electrochemical potential difference. It establishes a proton gradient of similar and often greater magnitude than the H(+)-ATPase on the same membrane. diphosphate + H(+)(in) + H2O = 2 H(+)(out) + 2 phosphate Monomer. Tonoplast. Has 16 transmembrane helices and a cytoplasmic domain that contains the active site. Has few direct interactions with pyrophosphate. Interacts with the substrate via divalent metal cations, such as magnesium ions, that are bound to the pyrophosphate (By similarity). Belongs to the H(+)-translocating pyrophosphatase (TC 3.A.10) family. K(+)-stimulated subfamily.