Kinetic properties of 5' nucleotidase in blood lymphocytes from healthy subjects, immunodeficient patients and cord blood.

The Km for AMP for 5' nucleotidase was increased in lymphocytes from patients with common variable (CVH) and sex linked (XLH) hypogammaglobulinaemia and from patients with chronic lymphatic leukaemia (CLL): the Vmax of the latter was low. The kinetic constants for cord blood lymphocytes are similar to adults and the Km does not change with age in lymphocytes from healthy adults. alpha-beta-Methylene adenosine diphosphate competitively inhibited 5' nucleotidase in lymphocytes from both healthy subjects and patients with CVH: the inhibitor constant (Ki) was higher for lymphocytes from patients with CVH than from control subjects. The concentration of zinc, an activator and modulator of 5' nucleotidase, was similar in control and CVH lymphocytes. It is concluded that lymphocyte 5' nucleotidase is functionally, abnormal in both primary hypogammaglobulinaemia and CLL and is deficient in the latter. These results provide support for the concept that CVH is a stem cell disease.