Proton-translocating inorganic pyrophosphatase that 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 Inhibited by excess pyrophosphate as well as excess Mg(2+). Inhibition by ATP, GTP, and CTP is reversed by increasing the Mg(2+) concentration. This suggests that the substrate is a particular metal complex such as MgPPi(2-). Modification of Asp-283 with DCCD abolishes pyrophosphatase activity. Homodimer. Tonoplast membrane. Detected in the hypocotyl, with the highest expression in the rapidly expanding segment of the hypocotyl and lower expression in older, less rapidly expanding parts of the hypocotyl. Has 16 transmembrane helices and a large 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. Belongs to the H(+)-translocating pyrophosphatase (TC 3.A.10) family. K(+)-stimulated subfamily.