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. The membrane bound form might support glycosylation reactions in the Golgi apparatus and, when released from cells, might catalyze the hydrolysis of extracellular nucleotides. 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. N-glycosylated. Belongs to the GDA1/CD39 NTPase family.