The kinetic properties of the ecto-ATPase of human peripheral blood lymphocytes and of chronic lymphatic leukemia cells

Abstract This study examines whether the activity of the Mg2+-dependent ecto- ATPase of the surface membrane of the human lymphocyte is changed in chronic lymphocytic B-cell leukemia (CLL-B) and may be an indicator of malignant transformation. The ecto-ATPase activities of preparations consisting predominantly of T or B cells were compared to each other and to the ecto-ATPase of the CLL peripheral blood lymphocytes (PBL). The specific activities and kinetic constants of the ecto-ATPase of the cell preparations were determined with [gamma-32P] adenosine triphosphate (ATP) as substrate. B-enriched lymphocytes had nearly fourfold greater specific activity and apparent Vmax than T-enriched lymphocytes, while the Km values of both cell types showed no significant difference. The specific activities and kinetic constants of the ecto-ATPase of the CLL PBL were significantly higher than the corresponding values of PBL or of B-enriched lymphocytes. Judging from the kinetic constants the ecto-ATPase of the CLL-B lymphocyte appears to be an enzyme that is distinctly different from that of the normal B cell. On the basis of the kinetic properties, the ecto-ATPase of the B cell appears to be identical with that of the T cell. The differences in the maximal velocities of the hydrolysis of ATP by B and T cells are likely due to a greater number of enzymatic sites on the B cell.