SPECIFICITY OF PYRIMIDINE NUCLEOSIDE PHOSPHORYLASES AND THE PHOSPHOROLYSIS OF 5-FLUORO-2'-DEOXYURIDINE

  • 1 January 1980
    • journal article
    • research article
    • Vol. 40  (3) , 507-511
Abstract
Isoelectric focusing and studies with 1-(2''-deoxy-.beta.-D-glucopyranosyl)thymine (GPT), a specific inhibitor of uridine phosphorylase activity, were used to determine the substrate specificities of mammalian pyrimidine nucleoside phosphorylases and their cleavage of 5-fluoro-2''-deoxyuridine (FdUrd). Isoelectric focusing profiles for the cytosol fractions from Ehrlich ascites cells and from Novikoff hepatoma cells each consisted essentially of 1 peak of nucleoside phosphorylase activity [isoelectric points (pI) 5.4 and 5.8, respectively] that cleaved uridine and thymidine (dThd) as well as FdUrd. Cytosol fractions from HeLa [human cervical carcinoma] (S3) cells, mouse liver and normal human leukocytes each exhibited a major peak of activity (pI 4.6, 6.5 and 4.9, respectively) that cleaved only dThd and FdUrd, while mouse liver exhibited a 2nd peak (pI 5.2) that cleaved primarily uridine. To distinguish clearly between uridine phosphorylases that cleave primarily uridine and that are inhibited by GPT, and dThd phosphorylases that cleave only deoxynucleosides and that are not inhibited by GPT, it is suggested that the term uridine-deoxyuridine phosphorylases be used to define those pyrimidine nucleoside phosphorylases that cleave uridine and dThd and that are inhibited by GPT. FdUrd apparently is cleaved to 5-fluorouracil by uridine-deoxyuridine phosphorylase activity in Ehrlich ascites cells and in Novikoff hepatoma cells, and by dThd phosphorylases in mouse liver, in normal human leukocytes and in HeLa (S3) cells. [The anti-neoplastic action of FdUrd was discussed.].