The function of ENTPD4 (ectonucleoside triphosphate diphosphohydrolase 4, ENSG00000197217) is as follows. [Isoform 1]: Catalyzes the hydrolysis of nucleoside triphosphates and diphosphates in a calcium- or magnesium-dependent manner, with a preference for pyrimidines. Preferentially hydrolyzes UTP and TTP. AMP, ADP, ATP and UMP are not substrates (PubMed:10858452, PubMed:9556635). Preferentially activated by Ca(2+) over Mg(2+) (PubMed:10858452). {ECO:0000269|PubMed:10858452, ECO:0000269|PubMed:9556635}. [Isoform 2]: Has a broad substrate specificity with the ability of cleaving all nucleotide di- and triphosphates with the exception of adenosine di- and triphosphate (ADP and ATP). Preferentially hydrolyzes CTP, UDP, CDP, GTP and GDP. Can use either Ca(2+) or Mg(2+) equally. {ECO:0000269|PubMed:10858452, ECO:0000269|PubMed:9556635}.