Cyclic 3'.5'-nucleotide phosphodiesterase. Effect of binding protein on the hydrolysis of cyclic AMP

The rate of cyclic AMP hydrolysis by a cyclic 3′,5′-nucleotide phosphodiesterase was diminished by the presence of a cyclic AMP binding protein in the reaction mixture. The reduction was proportional to the concentration of the binding protein; and was more pronounced at 0° than at 30°, presumably because the affinity of cyclic AMP to the binding protein was greater at 0° (“apparent dissociation constant” = 3 × 10⁻⁸ M) than at 30° (“apparent dissociation constant” = 4 × 10⁻⁷ M). These experiments indicate that cyclic AMP bound to the binding protein is not susceptible to the action of phosphodiesterase. It is hydrolyzed only when dissociated from the protein, and the rate of dissociation appears to be the limiting factor. The possible physiological significance of these results is discussed.