Maley 9316321 Deoxycytidylate deaminase provides a product which is essential as a substrate for thymidylate synthase and thus DNA synthesis. Any interference with the expression of either enzyme can result in a severe imbalance (toxicity) of nucleotide synthesis in the cell. An ultimate goal is to optimize toxicity in tumor cells and minimize the effect on normal cells. By understanding the properties and structure of these critical enzymes it may be possible to rationally design compounds which can achieve the above stated goal. Now, for the first time two sources (T4 and human) of deoxycytidylate deaminase are available and have been expressed in large enough quantities to begin x-ray crystallographic studies on their structure. Since deoxycytidylate deaminase is an allosteric enzyme very finely regulated within the cell and in vitro by its positive effector, dCTP, and its negative effector, dTTP, it provides the opportunity to clarify the mechanism of allosteric regulation. From the crystallographic data it may be possible to design better inhibitors of deoxcytidylate deaminase than those already available such as tetrohydrodeoxyuridylate and pyrimidine- 2-one deoxyribosemonophosphate. In any case better inhibitors could complement or synergize the action of thymidylate synthase inhibitors as well. Deoxycytidylate deaminase is a metalloprotein with 2 mols of zinc per subunit of the T4 enzyme and 1 mol of zinc per subunit of the human enzyme. Mutational studies will determine the binding sites for zinc in the two enzymes as well as the ligand binding sites. The crystallographic data will also contribute to location of the zinc atoms and different ligands within the sequence of the protein. An additional aspect of the current study involves the possible role of deoxycytidylate deaminase in stabilizing the T4 multienzyme aggregate, dNTP synthetase complex. %%% Deoxycytidylate diaminase catalyzes the conversion of dCMP to dUMP and thus provides an esse ntial substrate for thymidylate synthetase to produce dTMP. Since dTMP is absolutely required for DNA synthesis, its regulation is essential to cell growth and survival. In diverse organisms, deoxycytidylate deaminase is allosterically regulated by its end products, dCTP and dTTP, and plays a central role in determining the cellular balance of the nucleotides. ***
