Correlation between adenosine 3',5'-cyclic monosphosphate levels, adenylate cyclase activity, and adenosine 3',5'-cyclic monophosphate phosphodiesterase activity in tissue culture cells stimulated by serum.

Changes in the activity of adenylate cyclase [EC 4.6.1.1] of serum-stimulated hamster BHK cells in culture were investigated in relation to changes in the intracellular level of adenosine 3',5'-cyclic monophosphate (cyclic AMP). Addition of calf serum to quiescent cultures decreases the activity of adenylate cyclase, followed by cellular DNA synthesis. Cyclic AMP levels drop in parallel with the decrease in adenylate cyclase activity. Kinetic analysis of cyclic AMP phosphodiesterase [EC 3.1.4.17] revealed that BHK cells contain two forms of the enzyme, one with a Km of 0.77 muM and the other with Km of 17.0 muM. The activity of these enzymes is not affected by the addition of serum to tissue culture cells. The findings indicate that the decrease in adenylate cyclase activity is directly responsible for the decrease in cyclic AMP levels that is observed immediately after serum addition. Low levels of cyclic AMP continue for several hours during serum treatment, followed by a transient increase in cyclic AMP in the early stages of cellular DNA synthesis, at which time the activity of cyclic AMP phosphodiesterase with a low Km shows a slight decrease.