A simple and convenient assay method for phosphorolysis of 5'-deoxy-5-fluorouridine.

5'-Deoxy-5-fluorouridine (5'-DFUR) exhibits antitumor activity through its conversion to 5-fluorouracil by uridine phosphorylase (UPase) in mice. This mode of activation was confirmed by the fact that a mutant strain of Micrococcus flavus resistant to 5'-DFUR but sensitive to 5-fluorouracil was isolated and found to be deficient in UPase activity. Furthermore, since the enzyme level in tumor tissue should be useful as an indicator for therapy with 5'-DFUR, a simple assay method for the enzyme activity with use of the above bacterium was developed, in which the amount of 5-fluorouracil cleaved from 5'-DFUR by the enzyme was estimated through its antibacterial activity without separation from 5'-DFUR. This method is simple and efficient for handling a large number of samples.