Uridylate-cytidylate kinase

In a preparation from calf liver, Strominger et al. 13) achieved a partial separation of uridylate-cytidylate kinase activity from those for guanylate... 

Sugino el al. 17) have partly purified a deoxycytidylate kinase from calf thymus this preparation also phosphorylates cytidylate and uridylate, but not deoxyuridylate. The deoxyuridylate kinase activity was recovered in another protein fraction and so represents a distinct entity. As phosphate donors, only ATP and dATP were active in the cytidylate reaction. 

Thus, while existence of a cytidylate-deoxycytidylate kinase is established, there remains some uncertainty about the association of uridylate kinase activity with this enzyme. Phosphorylation of deoxyuridylate appears to be catalyzed by a separate enzyme activity, possibly by thymidylate kinase. 

Nelson and Carter 18) have purified thymidylate kinase about 5,000-fold from E. coli B and have shown that thymidylate was phosphorylated about seven times faster than deoxyuridylate. Uridylate was not a substrate, nor were adenylate, guanylate, cytidylate, or their deoxyribosyl counterparts. This enzyme was less specific for the triphosphate phosphoryl donor than the kinases previously discussed, because CTP, GTP, and the corresponding deoxyribonucleotides also served as phosphate donors, although less weU than ATP. 

GTP AMP phosphotransferase GTP-adenylate kinase U ridylate-cytidy late kinase Uridylate kinase Cytidylate-deoxy-c)rtidylate kinase... 

Fractionation of extracts from calf thymus for kinase activity toward deoxyribonucleoside monophosphates has revealed the presence of at least four separate enzymes the kinase activities for dAMP, dGMP, dCMP, and dTMP are separate entities in this tissue 31). Each has been partly purified and examination of substrate specificities showed that the kinases for deoxyadenylate and deoxyguanylate also phosphorylate the ribosyl homologues, adenylate and guanylate, respectively. The deoxycytidylate kinase accepts as substrates both cytidylate and uridylate, but will not phosphor> late deoxyuridylate. The calf thymus thymidine monophosphate... 

As a further instance of a dual function for the nucleoside monophosphate kinases, separate kinases for adenylate-deoxyadenylate, guanylate-deoxyguanylate, cytidylate-deoxycytidylate, uridylate, and thynudylate have been demonstrated in E. cdi extracts (35) it should be noted that cytidylate-deoxycytidylate kinase and uridylate kinase were found as separate enzyme activities in the E. cdi experiments. 

UMP in a reaction that greatly resembles that of adenylate kinase. The reaction requires ATP and results in the formation of ADP and UDP. The complete purification of kinases of this type has not been achieved, but the partial separations already accomplished indicate that at least three, and possibly more enzymes with varying substrate specificities exist. These enzymes, studied in calf liver extracts, all use ATP as the phosphate donor, and show at least relative specificity for adenylic acid, uridylic acid, and cytidylic acid as phosphate acceptors. 

---