Characterization of protein phosphorylation in acetylcholine receptor-enriched membrane preparations from torpedo fuscomaculata

Summary Erythrocyte soluble phosphodiesterase activities show at least two interconvertible states: aggregated and non-aggregated. In the former state the existence of a high affinity component for cyclic AMP is favoured and the system is more active with cyclic AMP than with cyclic GMP as substrate. When the system is in the non-aggregated state, no activity with cyclic GMP is detected. Conversion to the non-aggregated state is enhanced by dilution or by addition of magnesium ions.Upon isoelectric focusing of erythrocyte soluble extracts, phosphodiesterase activities can be resolved in two peaks: one specific for cyclic AMP located at pH 4.66 and the other specific for cyclic GMP focused at pH 4.95. Evidence would indicate that aggregation affects the enzyme specific for cyclic AMP.