Deoxycytidine kinase is constitutively expressed in human lymphocytes: consequences for compartmentation effects, unscheduled DNA synthesis, and viral replication in resting cells.

Deoxycytidine kinase specific activity was high in human peripheral lymphocytes and increased less than 2-fold when the lymphocytes were stimulated by phytohemagglutinin A. Ion-exchange chromatography showed the same profile of deoxycytidine kinase activity in resting and proliferating cells. This enzyme could also efficiently phosphorylate deoxyadenosine and deoxyguanosine. In contrast, the thymidine kinase activity was very low in resting peripheral lymphocytes and increased more than 40-fold upon stimulation. Similar relative changes in the activities of the two enzymes were observed in human T-lymphoblast cells (CCRF-CEM) separated by centrifugal elutriation into cells of different cell cycle phases. The ratio of deoxycytidine to thymidine kinase activities is 20:1 in extracts from resting human lymphocytes and 1:2 in PHA-stimulated cells. This drastic change in deoxyribonucleoside phosphorylating activities during the cell cycle in human lymphocytes is of importance for studies on unscheduled DNA synthesis, for the design of therapies to interfere with viral DNA metabolism, and for a correct interpretation of the compartmentation effects observed in DNA precursor metabolism.