Further Studies of the Interaction of Cyclic Adenosine 3′:5′-Monophosphate with Endometrial Protein Kinase

Purification of the adenosine cyclic 3':5'-monophosphate (cAMP)-dependent protein kinase of bovine endometrium and its binding and catalytic subunits has permitted study of their kinetic and equilibrium interaction with cAMP. Data obtained at physiological pH were compared with those previously noted at pH 5.0 where the cAMP-protein kinase interaction is optimal. Reactions utilizing the binding subunit exhibited second order association kinetics and temperature dependence. The second order rate constant was dependent on [cAMP]0, an anomaly previously noted at pH 5.0. Reactions using the cAMP-dependent protein kinase exhibited nonlinear second order plots with little temperature dependence. The dissociation process was substantially faster at pH 7.4 and appeared to be biphasic. Thus, the reaction between cAMP and its receptor in the presence or absence of the catalytic subunit exhibited qualitatively similar behavior at pH values of 5.0 and 7.4.