SYNTHESIS OF 5-FLUOROURIDINE 5'-PHOSPHATE BY A PYRIMIDINE PHOSPHORIBOSYLTRANSFERASE OF MAMMALIAN ORIGIN .I. SOME PROPERTIES OF ENZYME FROM P1534J MOUSE LEUKEMIC CELLS

Cell-free extracts of PI534J mouse leukemic cells catalyze the synthesis of 5-fluorouridine 5′-phosphate from 5-fluorouracil and 5-phosphoribosyl 1-pyrophosphate. The product was identified by its migration during paper chromatography in three different solvent systems. This enzymatic reaction requires the presence of a divalent cation and is inhibited by inorganic pyrophosphate but not by orthophosphate. These results suggest that the synthesis of 5-fluorouridine 5′-phosphate is catalyzed by a pyrimidine phosphoribosyltransferase. The enzyme exhibits a pH optimum of 10 and shows maximal activity in the presence of Mg2+ although Mn2+, Co2+, and Ca2+ support substantial reaction rates. Neither Hg2+, nor Zn2+, nor Cu2+ is able to substitute for Mg2+. The Km values are 83 μM for 5-fluorouracil and 120 μM for 5-phosphoribosyl 1-pyrophosphate. Evidence indicating that the enzyme can also utilize uracil and possibly orotic acid as substrates for synthesis of the corresponding ribonucleotide is presented. © 1969, American Chemical Society. All rights reserved.