Short-Term Binding and Hydrolysis of Cyclic 3′:5′-Adenosine Monophosphate by Aggregating Dictyostelium Cells

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Abstract
Transient binding of cyclic AMP to aggregating cells of Dictyostelium discoideum was measured under cyclic GMP excess in order to inhibit cyclic AMP hydrolysis by cell-bound phosphodiesterase. Cyclic GMP extended the period of half-maximal cyclic AMP binding from less than 5 sec to 1-2 min. With the same time course as bound cyclic AMP was released from the cells, labeled 5'-AMP appeared in the medium. Specificity, kinetics, and developmental regulation suggest that the cyclic AMP-binding sites exposed in living cells are identical with receptor sites for the chemotactic response. The functioning of the cyclic AMP-receptor/phosphodiesterase system and its formal similarity with the synaptic acetylcholine-receptor/esterase system are discussed.