Purine nucleoside phosphorylases purified from rat liver and novikoff hepatoma cells

Abstract

Purine nucleoside phosphorylase (PNP) was purified from rat hepatoma cells and normal liver tissue utilizing the techniques of ammonium sulfate fractionation, heat treatment, ion-exchange and molecular exclusion chromatography, and polyacrylamide gel electrophoresis. Homogeneity was established by disc gel electrophoresis in the presence and absence of sodium dodecyl sulfate. Purified rat hepatoma and liver PNPs appeared to be identical with respect to subunit and native molecular weight, substrate specificity, heat stability, kinetics and antigenic identity. A native molecular weight of 84,000 was determined by gel filtration. A subunit molecular weight of 29,000 was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A single isoelectric point was observed at pH 5.8, and the pH optimum was 7.5. Inosine, guanosine, xanthosine, and 6-mercaptopurine riboside were substrates for the enzymes. The apparent K m for both inosine and guanosine was about 1.0 × 10 −4 m and for phosphate was 4.2 × 10 −4 m. Hepatoma and liver PNP showed complete cross-reactivity using antiserum prepared against the liver enzyme.