Pyrimidine phosphorylase is an enzyme of the nucleoside salvage pathway. It catalyzes the phosphorolysis of selected nucleosides to the corresponding base and a-D-ribose-1-phosphate. In lower organisms pyrimidine phosphorylase uses both uridine and thymidine as substrates, while in higher organisms such as mammals there is an enzyme that accepts thymidine and an enzyme that accepts uridine. In humans the enzyme not only catalyzes the phosphorolysis of pyrimidines, but also plays a role in tumor angiogenesis. Pyrimidine phosphorylase has also been implicated in the activation of the prodrug 5-fluoro-2-deoxyuridine. Pyrimidine phosphorylase has been purified from beef liver by a combination of techniques including ammonium sulfate fractionation, ion exchange chromatography, hydroxyapatite chromatography, and size exclusion chromatography. The substrate specificity along with the Michaelis constant and turnover number were determined for a number of nucleoside analogs. These analogs were also tested for their ability to inhibit the enzyme. Physical characteristics such as subunit size, native molecular weight, and isoelectric point have been determined.

Purification and characterization of beef liver pyrimidine phosphorylase

247th National Meeting (2014)

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