Abstract
The phosphorylation of 5-substituted deoxycytidine analogues by deoxycytidine kinase was studied in extracts of mouse and human lymphoid cells. The apparent Km for the phosphorylation of 5-bromodeoxycytidine in extracts of mouse lymphoma cells was 2.0 mM, in contrast to a Km of 10 µM for deoxycytidine phosphorylation. The apparent Km for the phosphorylation of 5-methyldeoxycytidine by the mouse enzyme was 80 µM. The affinity of mouse deoxycytidine kinase for 5-iododeoxycytidine was lower than for 5-bromodeoxycytidine, whereas its affinity for 5-fluorodeoxycytidine was similar to that for deoxycytidine. With human deoxycytidine kinase the apparent Km was 0.4 mM for 5-bromodeoxycytidine, as compared to 2.0 µM for deoxycytidine. These results suggest that the activity of deoxycytidine kinase is affected by the size of substitutions in position 5 of its substrate. This restricted substrate specificity of deoxycytidine kinase could limit the utilization of 5-bromodeoxycytidine for DNA synthesis.
ACKNOWLEDGMENT We are grateful to Ira Schildkraut for helpful discussions and suggestions and critical reading of the manuscript.
- Copyright ©, 1973, by Academic Press, Inc.
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