Abstract
Rat brain type II (β) protein kinase C (PKC) was phosphorylated by rat lung casein kinase II (CK-II). Neither type I (γ) nor type III (α) PKC was significantly phosphorylated by CK-II. CK-II incorporated 0. 2-0. 3 mol of phosphate into 1 mol of type II PKC. This phosphate was located at the single seryl residue (Ser-11) in the V1-variable region of the regulatory domain of the PKC molecule. A glutamic acid cluster was located at the carboxyl-terminal side of Ser-11, showing the consensus sequence for phosphorylation by CK-II. The velocity of this phosphorylation was enhanced by the addition of Ca2+, diolein, and phosphatidylserine, which are all required for the activation of PKC. Phosphorylation of casein or synthetic oligopeptides by CK-II was not affected by Ca2+, diolein, or phos-phatidylserine. Available evidence suggests that CK-II phosphorylates preferentially the activated form of type II PKC. It remains unknown, however, whether this reaction has a physiological significance.
