[40] Uridine-cytidine kinase from a murine neoplasm

Publisher Summary This chapter describes the purification procedure of uridine–cytidine kinase from a Murine Neoplasm. Uridine–cytidine kinase is part of the anabolic pathway by which the preformed pyrimidine nucleosides are salvaged for nucleic acid biosynthesis. In mammalian cells, the enzymic activity is, especially high in cells exhibiting a rapid rate of growth. This kinase is apparently the rate-limiting step in the conversion of the nucleosides to their respective triphosphates and is susceptible to feedback regulation by both citrate transport protein (CTP) and uracil triphosphate (UTP). In Salmonella typhimurium , uridine–cytidine kinase does not appear to be an inducible enzyme. In less pure preparations, a specific assay employs the conversion of radioactive substrate to product, with the chromatographic isolation of the products formed. Only uridine and cytidine, among the normal, physiological nucleosides, appear to be phosphorylated by this enzyme. In contrast, thymine riboside, the deoxyribosides, and cytosine arabinoside are not substrates. Adenosine, purine deoxyribosides, uridine monophosphate (UMP) synthetase, and cytidine monophosphate (CMP) are also not phosphorylated.