Mechanism of proteolytic activation of rat liver protein kinase C generating Ca2(+)-phospholipid-independent form with apparent molecular mass of 80,000.

1. New Ca2(+)-phospholipid-independent form of protein kinase C was produced by limited proteolysis with trypsin. 2. The molecular mass of this active enzyme was slightly smaller than that of original protein kinase C. 3. The active enzyme cross-reacted with antibody against the pseudosubstrate region on amino-terminal end of protein kinase C. 4. The active enzyme was inhibited by the peptide inhibitor derived from the pseudosubstrate region. 5. These results suggest that the limited proteolysis at or near the pseudosubstrate region made protein kinase C active without Ca2+ and phospholipid.