The single NTPase gene of Drosophila melanogaster encodes an intracellular nucleoside triphosphate diphosphohydrolase 6 (NTPDase6)

I report here the cloning and characterization of a nucleoside triphosphate diphosphohydrolase 6 (NTPDase6) encoded by the single Dmel/NTPase gene of Drosophila melanogaster. S2 cells stably transfected with the Drosophila NTPDase6 cDNA displayed strong UDPase activity only after addition of NP-40, indicating the intracellular location of the enzyme. The enzyme hydrolyzed UDP, GDP, and IDP equally well whereas other NDP and NTP were poor substrates. It was not or only partially inhibited by several modulators of the cell surface NTPDases, but was strongly inhibited upon oxidative cross-linking by copper phenanthroline. The decrease of activity correlated with dimer formation. Mutagenesis studies indicated that dimer formation required C42 in the transmembrane domain and C447 in the exoplasmic domain. Fluorescence microscopy revealed that the protein was located primarily in the ER. The substrate specificity and cellular localization of the Drosophila NTPDase6 suggest that it participates in Drosophila glycoprotein processing.