Catalyzes the hydrolysis of inorganic polyphosphate (polyP) chains of many hundreds of phosphate residues into shorter lengths both by cleaving phosphate from the chain end and by fragmenting long-chain polymers into shorter ones. The limited digestion products are 1 and 3 P(i) residues (PubMed:11102525, PubMed:11447286, PubMed:15170373, PubMed:15342119, PubMed:15792812, PubMed:8900207, Ref.16). Also releases phosphate from dATP. dATP phosphohydrolase activity is about 7-fold lower than the exopolyphosphatase activity (Ref.16). [phosphate](n+1) + n H2O = n H(+) + (n+1) phosphate [phosphate](n) + H2O = [phosphate](n-1) + H(+) + phosphate dATP + H2O = dADP + H(+) + phosphate Divalent metal cations. Exopolyphosphatase activity is predominant in the presence of Co(2+), while endopolyphosphatase activity is predominant in the presence of Mg(2+) (PubMed:8900207, PubMed:25742176). Co(2+) is more effective than Mn(2+) for dATP phosphohydrolase activity (Ref.16). Inhibited by heparin and EDTA. Optimum pH is about 7.5. Homotetramer. The cytoplasmic form appears in the cytosol during the transition of cells from stationary growth phase to new budding on glucose addition and phosphate excess. The transmembrane domain contains polar residues that mediate the recognition by TUL1. Processing by proteases in the vacuole is required for activation. Ubiquitinated. Ubiquitination mediates sorting into internal vesicles in late endosomes. TUL1 and RSP5 are required for ubiquitination. Other cytoplasmic Lys residues than Lys-6 may also be ubiquitinated. N-glycosylated (Probable). N-glycosylation is essential for the protease-mediated maturation. Inactivation of PPN1 leads to the inhibition of expression of both exopolyphosphatase PPX1 and high-molecular-mass exopolyphosphatase not encoded by PPX1. Present with 319 molecules/cell in log phase SD medium. Belongs to the endopolyphosphatase PPN1 family.