Properties of hepatic and pancreatic cyclic AMP phosphodiesterase in the cat.

Cyclic adenosine-3',5'-monophosphate phosphodiesterase has been characterized in homogenates of feline pancreas and liver. The cyclic AMP phosphodiesterase of feline liver showed a pH optimum at 7.8-7.9. In contrast, cyclic AMP phosphodiesterase activity of feline pancreas increased at up to pH 8.8 without attaining a peak. Hepatic cyclic AMP phosphodiesterase appeared to possess two different enzyme activities, a high and a low affinity form for cyclic AMP. The Michaelis constant for this enzyme was 0.567 and 85.6 microM, respectively. The maximal velocity of this enzyme was 0.135 and 2.84 nmol cyclic AMP hydrolyzed per mg of protein per min. The presence of multiforms of pancreatic cyclic AMP phosphodiesterase was neither demonstrated nor excluded. The kinetics constant for this enzyme for a one-enzyme model without cooperativity was 5.30 microM, and the maximal velocity was 4.97 nmol cyclic AMP hydrolyzed per mg of protein per min.