ADP‐Ribosylation of Nuclear Proteins in Normal Lymphocytes and in Low‐Grade Malignant Non‐Hodgkin Lymphoma Cells

Normal lymphocytes and lymphocytes from patients with low‐grade malignant non‐Hodgkin lymphoma were isolated from blood by a Percoll gradient procedure. Absence of cell proliferation in both cell types was indicated by very low [ 3 H]thymidine incorporation rates. Determination of endogenous protein‐bound single ADP‐ribose residues by a radioimmunoassay revealed that the leukemic cells had 2.5‐times lower levels of the NH 2 OH‐sensitive and a 4‐fold lower amount of NH 2 OH‐resistant ADP‐ribose · protein conjugate subfractions, respectively, than normal lymphocytes. By contrast, ‘total’ ADP‐ribose transferase activity, as measured in homogenates or permeabilized cells in the presence of DNase, was two‐times higher in leukemic cells, whereas activity determined in permeabilized cells in the absence of added DNase was practically identical in both cell types. The apparent discrepancy between ADP‐ribose transferase activity and endogenous levels of protein‐bound single ADP‐ribose residues may be explained in part by an enzyme inhibitor present in normal human lymphocytes. NAD + NADH levels were decreased 2.5‐fold in the leukemic cells. This decrease, however, does not explain the reduced levels of mono(ADP‐ribose) · protein conjugates since the ratio of protein‐bound single ADP‐ribose residues to NAD is distinctly different in leukemic lymphocytes compared to normal lymphocytes.