Human Lymphocytic Ecto-5′-NT: Its Determination and Partial Characterization

Abstract

The enzyme purine 5′-nucleotidase (ecto-5#x2032;-NT, EC.3.1.3.5) located on the outer membrane of cells (e.g. lymphocytes), catalyses the hydrolysis of the phosphate group from purine mononucleotides. This ecto-enzyme can serve as a marker of T- and B-cell maturation(1,2,3). So far little is known about kinetic properties of ecto-5′-NT on human lymphoid cells. Controversial results have been published about ecto-5′-NT activities on human peripheral blood lymphocytes (PBL). These may be attributed to differences in assay conditions such as choice of proper substrate, the use of different concentrations of Mg²⁺ the use of α, ß-methylene adenosine diphospho-nate (AOPCP) as a specific inhibitor of ecto-5′-NT activity and the concentration of this compound in the assay. In the present study we investigated kinetic properties and substrate specificity of the enzyme on intact human PBL in addition to the inhibition by AOPCP as well as the influence of Mg²⁺. Furthermore, we determined ecto-5′-NT activities on normal PBL and on lymphocytes from patients with immunodeficiency diseases, including a patient with purine nucleoside Phosphorylase deficiency (4). Also the amount of ecto-5′-NT enzyme protein was determined on lymphocytes of the latter patient.