Properties of uridine-cytidine kinase derived from L1210 leukemia cells

Uridine-cytidine kinase isolated from murine L1210 leukemia cells exist in several isozymic forms, as indicted by isoelectric focusing and by column chromatography on Sepharose 6B. Of 39 compounds thus far examined as potential inhibitors of the phosphorylation of uridine by ATP, four were of significant activity: 5'-azido-5'-deoxycytidine, 5'-O-nitro-5-fluorouridine, 5'-O-nitrouridine, and 5'-azido-5'-deoxyuridine. 5'-Azido-5'-deoxycytidine was the most active (competitive with uridine) and exhibited a Ki of 37 x 10(-5) M. Other properties of uridine-cytidine kinase were examined, and the apparent Michaelis constants for uridine, cytidine, and adenosine 5'-triphosphate were 23 x 10(-5) M, 15 x 10(-5) M, and 34.9 x 10(-5) M, respectively.