Protein kinase C inhibits the Ca(2+)-dependent stimulation of phospholipase C-beta 1 in vitro

Protein kinase C (PKC) inhibited the Ca(2+)-dependent stimulation of a 600-fold purified phospholipase C beta 1 (PLC-beta 1). Inhibition by PKC was time-dependent, and required ATP and diacylglycerol. Inhibition was more pronounced when the PLC assay was conducted with a PIP2 substrate mixture containing phosphatidylserine, then with a substrate mixture containing phosphatidyle-thanolamine. Cyclic AMP-dependent protein kinase A did not inhibit PLC-beta 1 activity. PKC did not affect the rate of PLC-beta 1 activation by Ca2+ or the rate of PLC-beta 1 deactivation by EGTA. PLC-beta 1 purified 1700-fold was less sensitive to inhibition by PKC despite stoichiometric phosphorylation. These results demonstrate that PKC inhibits the Ca(2+)-dependent stimulation of a 600-fold purified PLC-beta 1 in vitro. Furthermore, purification of PLC-beta 1 to homogeneity results in a diminished sensitivity to inhibition by PKC, indicating that other components may participate in mediating the effect of PKC on the Ca(2+)-dependent stimulation of PLC-beta 1 in vitro.