Endogenous protein kinase inhibitor levels regulate changes in specific activity of protein kinase in quiescent cells stimulated to proliferate

Abstract

Following serum stimulation of quiescent Chinese hamster ovary cells, changes in the total specific activity of cAMP-dependent protein kinase were inversely related to the cellular levels of heat stable inhibitor(s) of this enzyme. During the initial 2 hrs. after stimulation, a rapid 2-fold decrease in the specific activity of protein kinase occurred, together with a 2-fold increase in the intracellular levels of protein kinase inhibitor(s). Similarly while protein kinase activity increased from 3 to 5 hrs, and decreased from 5 to 7 hrs. after stimulation, inhibitor(s) levels declined and then rose. These and other observations discussed below support the hypothesis that the heat stable inhibitor(s) have physiological functions in regulating the total intracellular pools of cAMP-dependent protein kinase.