Thymidine kinase, deoxycytidine kinase and deoxycytidylate deaminase activities in phytohaemagglutinin stimulated human lymphocytes.

The aim of this study was to determine the changes of thymidine kinase, deoxycytidine kinase and deoxycytidylate deaminase activity of normal human lymphocytes following phytohaemagglutinin (PHA) stimulation and the effect of actinomycin D on the activities of these enzymes. DNA synthesis, monitored with pulses of 3H-thymidine, began to increase at about 24 h after PHA addition and reached a broad peak at about 60 h. During this time period the ability of the cell extracts to phosphorylate TdR and CdR and to deaminate dCMP also increased several times above the control levels with peaks of activity between 50 and 70 h; the peak of thymidine kinase activity was delayed with respect to that of DNA synthesis. Actinomycin D added during the first 30 h of culture completely inhibited the subsequent increase of the enzyme activities assayed at 58 h after PHA, but had no effect when added later than 48–52 h.