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Abstract: Nucleoside triphosphate diphosphohydrolase 3 (NTPDase3) is a cell surface, membrane-bound enzyme that hydrolyzes extracellular nucleotides, thereby modulating purinergic signaling. An alternatively spliced variant of NTPDase3 was obtained and analyzed. This alternatively spliced variant, termed “NTPDase3β”, is produced through the use of an alternative terminal exon (exon 11) in place of the terminal exon (exon 12) in the full-length NTPDase3, now termed “NTPDase3α”. This results in an expressed protein lacking the C-terminal cytoplasmic sequence, the C-terminal transmembrane helix, and apyrase conserved region 5. The cDNA encoding this truncated splice variant was detected in a human lung library by PCR. Like the full-length NTPDase3α, the alternatively spliced NTPDase3β was expressed in COS cells after transfection, but only the full-length NTPDase3α is enzymatically active and properly trafficked to the plasma membrane. However, when the truncated NTPDase3β was co-transfected with full-length NTPDase3α, there was a significant reduction in the amount of NTPDase3α that was properly processed and trafficked to the plasma membrane as active enzyme, indicating that the truncated form interferes with normal biosynthetic processing of the full-length enzyme. This suggests a role for the NTPDase3β variant in the regulation of NTPDase3 nucleotidase activity, and therefore the control of purinergic signaling, in those cells and tissues expressing both NTPDase3α and NTPDase3β. [Copyright &y& Elsevier]