Cyclic AMP Phosphodiesterase Activities in Xenopus laevis Oocytes

Cyclic AMP phosphodiesterase activity has been identified in full-grown Xenopus oocytes in vivo and in vitro. About 50% of the in vitro phosphodiesterase activity was present in the soluble fraction and 35% in a partially purified membrane fraction. Both activities exhibited high substrate affinity (Km about 10⁻⁶ M). Sucrose gradient fractionation revealed two forms of phosphodiesterase: a 5 S form (peak I) and a 6.5 S form (peak II). Treatment with trypsin led to the activation of the soluble enzyme with the transformation of peak II into peak I.
Ethylene glycol bis (β-aminoethyl ether)-N,N'-tetraacetic acid, calcium dependent regulator, and Fluphenazine did not influence the enzyme activities suggesting that the oocyte phosphodiesterases were not Ca²⁺-dependent. Intact oocytes were induced to mature by exposure to progesterone; their phosphodiesterase activities and distribution tested in vitro were comparable to those of untreated oocytes.