SUBSTRATE-SPECIFICITY OF ESCHERICHIA-COLI THYMIDINE PHOSPHORYLASE FOR PYRIMIDINE NUCLEOSIDES WITH ANTI-HUMAN-IMMUNODEFICIENCY-VIRUS ACTIVITY

Various nucleoside antiviral agents and their metabolites were examined for their ability to be cleaved across the glycosidic bond by Escherichia coli thymidine phosphorylase. The increasing order of susceptibility to cleavage was U > T >> C derivatives. Nucleosides that were unsaturated in the sugar moiety were more susceptible than saturated ones. 3'-Deoxy-2',3'-didehydrothymidine was a substrate, whereas 3'-azido-, 3'-fluoro-, 3'-oxo- and 3'-thiapyrimidine nucleosides were resistant to this enzyme.