CD39 IS AN ECTO-(CA2+,MG2+)-APYRASE

CD39, a 70- to 100-kDa molecule expressed primarily on activated lymph oid cells, was previously identified as a surface marker of Epstein Ba rr virus (EBV)-transformed B cells. In this report, we show that an ec to-(Ca2+,Mg2+)-apyrase activity is present on EBV-transformed B cells, but not on B or T lymphomas. The coincidence between CD39 expression and ecto-apyrase activity on immune cells suggests that CD39 may be an ecto-apyrase. This supposition is supported by the observation that t he amino acid sequence of CD39 is significantly homologous to those of several newly identified nucleotide triphosphatases. Finally, we show that CD39 indeed has ecto-apyrase activity by expression in COS-7 cel ls.