Abstract

A purine-nucleoside phosphorylase (purine-nucleoside:orthophosphate ribosyltransferase, EC 2.4.2.1) from bovine thyroid tissue has been purified 670-fold utilizing the techniques of ammonium sulfate precipitation, ion-exchange and molecular-exclusion chromatography, and polyacrylamide-gel electrophoresis. The protein has an apparent molecular weight of 90,000, a single isoelectric point at 5.6, and a Michaelis constant of 0.028 m m for inosine. Double-reciprocal plots of the reaction rate for the phosphorylase-catalyzed reaction versus phosphate or arsenate concentration display a downward trend at high substrate concentrations. Two apparent Michaelis constants of 0.38 and 1.49 m m were determined for phosphate.

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