Uridine Phosphorylase 1 (UPP1)

The 2 known types of pyrimidine nucleoside phosphorylases, uridine phosphorylase (UP; EC 2.4.2.3) and thymidine phosphorylase (TP; EC 2.4.2.4), in the presence of orthophosphate, catalyze the reversible phosphorolysis of uridine and thymidine or deoxyuridine, respectively, to free bases and ribose-1-phosphate or deoxyribose-1-phosphate.The recombinant UP expressed in COS-7 cells demonstrated specific enzyme activity with uridine as the substrate; this activity was inhibited by a competitive inhibitor. Northern blot analysis with the cDNA as a probe demonstrated high levels of mRNA expression in several tumor cell lines but a very low level in a normal cell line.