Has a threefold preference for the hydrolysis of ATP over ADP. a ribonucleoside 5'-triphosphate + 2 H2O = a ribonucleoside 5'-phosphate + 2 H(+) + 2 phosphate Expressed in adult brain, pancreas, spleen and prostate (PubMed:9676430). Moderate or low expression is seen in most tissues (PubMed:9676430). Not expressed in liver and peripheral blood leukocytes (PubMed:9676430). Belongs to the GDA1/CD39 NTPase family.