Some properties of adenosine 3′,5′-cyclic monophosphate phosphodiesterase in the superior cervical ganglion of the guinea pig

摘要

Adenosine 3′,5′-cyclic monophosphate (cAMP) phosphodiesterase activity in crude guinea-pig superior cervical ganglion homogenates was assayed under a variety of experimental conditions. Two forms of cAMP phosphodiesterase were found, one with high and the other with low affinity for the substrate. TheKmvalues were about 1 and 110 μM respectively. Imidazole slightly but constantly stimulated the former enzyme form over a wide range of concentrations and l-methyl-3-isobutylxanthine was a weak competitive inhibitor with aKivalue of 90 μM. Low affinity cAMP phosphodiesterase activity was increased by calmodulin and Ca2+. This stimulation was not observed in the presence of trifluoperazine, a specific inhibitor of calmodulin. On the other hand, neither d-Ala2met-enkephalinamide nor prostaglandin E2, alone or in combination, influenced high affinity cAMP phosphodiest