Ectonucleoside Triphosphate Diphosphohydrolase 4 (ENTPD4)

LYSAL1 increased the intracellular membrane-bound nucleoside phosphatase activity. Activity was highest with UDP as substrate, and it was stimulated by divalent cations, particularly Ca(2+). UDP hydrolysis increased in the presence of detergents or alamethicin, an ionophore that facilitates movement of UDP across the membrane, suggesting that the active site of LYSAL1 is on the luminal side of the Golgi apparatus.The deduced 609-amino acid protein, which they called Golgi luminal UDPase, contains apyrase conserved regions and 2 transmembrane domains. There are 2 potential N-glycosylation sites between the transmembrane domains. Northern blot analysis revealed transcripts of 3.0, 3.2, and 7.5 kb expressed in all tissues examined.