Pyrimidine Nucleoside Phosphorylases of Rat Liver SEPARATION BY ION EXCHANGE CHROMATOGRAPHY AND STUDIES OF THE EFFECT OF CYTIDINE OR URIDINE ADMINISTRATION

摘要: Abstract By chromatography on diethylaminoethyl Sephadex, three enzyme fractions with pyrimidine nucleoside phosphorylase activity have been separated from extracts of normal or regenerating liver rats. Two these probably represent isoenzymes uridine phosphorylase. Both are phosphate-dependent and both exhibit maximal activities toward uridine, deoxyuridine, thymidine at pH values 7.9 to 8.2, 6.4 6.8, 5.6 5.8, respectively. One isoenzyme is nuclear origin, whereas the other predominantly cytoplasmic origin. At optimum respective substrates, as well physiological pH, catalyze phosphorolysis a more rapid rate than deoxyuridine much less active thymidine. The third enzyme, phosphorylase, mainly It also phosphate-dependent; it most 5.8 5.4, but shows no deoxycytidine. has deoxyuridine- thymidine-cleaving over range studied, responsible for catalyzing in cells. Under standard conditions assay specific phosphorylases were found be increased about 3-fold when assayed presence 6 hours after injection uridine. Six cytidine enzymes each substrates 2-fold. Concomitantly, was not changed by decreased cytidine.