Catalyzes the hydrolysis of nucleoside triphosphates and diphosphates in a calcium- or magnesium-dependent manner. Has a strong preference for nucleoside diphosphates, preferentially hydrolyzes GDP, IDP, and UDP, with slower hydrolysis of CDP, ITP, GTP, CTP, ADP, and UTP and virtually no hydrolysis of ATP (PubMed:11042118). The membrane bound form might support glycosylation reactions in the Golgi apparatus and, when released from cells, might catalyze the hydrolysis of extracellular nucleotides (PubMed:11042118). a ribonucleoside 5'-diphosphate + H2O = a ribonucleoside 5'-phosphate + H(+) + phosphate H2O + IDP = H(+) + IMP + phosphate GDP + H2O = GMP + H(+) + phosphate H2O + UDP = H(+) + phosphate + UMP Strongly and equally activated by either Ca(2+) or Mg(2+). Exists as a secreted and membrane-bound forms in the medium of transfected cells, the secreted form is predominant. Expressed in heart and brain. Might be cleaved at the N-terminus, retained in an intracellular membrane compartment and in addition be released into the extracellular medium. N-glycosylated. Belongs to the GDA1/CD39 NTPase family.