Properties and distribution of cyclic AMP phosphodiesterase from rat liver.

1. Phosphodiesterase activity in rat liver supernatant and solubilized rat liver particulate fractions was chromatographed on Q Sepharose and several characteristics of each peak determined. 2. Rat liver supernatant contained four peaks of activity. The first two of these corresponded to type I and II phosphodiesterases. The fourth peaks was similar to a type V activity and the third peak could not be definitely classified. 3. Particulate activity solubilized by mild protease treatment also contained four peaks of activity. The first two corresponded to the first two from the supernatant, the fourth was a type IV enzyme which is the insulin activated phosphodiesterase. The third peak could not be definitely characterized. 4. Particulate activity solubilised by Triton X-100 contained three peaks. Two had the properties of a type IV enzyme but only one of these was immunologically identified as the insulin sensitive enzyme. The remaining activity was similar to the chymotrypsin peak 3 activity. 5. Most of the particulate phosphodiesterase of rat liver is found in a microsomal fraction, and most is the insulin sensitive type IV enzyme.

Phosphorylation of hormone sensitive phosphodiesterase in isolated adipocytes.

Cyclic AMP phosphodiesterase in rat adipocytes is stimulated by insulin and also by agents that increase cyclic AMP levels. When the enzyme is immunoprecipitated from a solubilised microsomal preparation from adipocytes prelabelled with radioactive phosphate and separated on SDS polyacrylamide gels, label is found in a protein band at the expected Mr for adipose tissue phosphodiesterase. Treatment of the adipocytes with isoproterenol or methyl isobutylxanthine increased the labelling of this band. Insulin alone had no effect on its labelling but did decrease the incorporation of label caused by isoproterenol.