Phosphodiesterase II in epithelial cells from guinea-pig and rat small intestine

Phosphodiesterase II activity was determined by using a synthetic substrate, the 2,4-dinitrophenyl ester of thymidine 3'-phosphate. The enzyme activity was determined in fractions obtained by differential centrifugation of homogenates of epithelial cells from the small intestinal mucosa of guinea pigs and rats. In guinea-pig preparations phosphodiesterase II occurred with highest specific activity in those fractions rich in succinate dehydrogenase and acid phosphatase. A lysosomal location for the guinea-pig enzyme was indicated by its structure-linked latency and by its association with particles that under-went a characteristic decrease in equilibrium density when Triton WR-1339 was injected into the animals. With rat preparations a much greater proportion of the phosphodiesterase II activity was found in the soluble fraction after ultracentrifugation. The rat enzyme exhibited a lower degree of latency and administration of Triton WR-1339 had no effect. The rat enzyme further differed from that of the guinea pig in other respects; it was more labile at 60 degrees C, it exhibited a lower pH optimum and it had a higher molecular weight as determined by gel-filtration chromatography.