Protein kinase C stimulatory activity in the pseudopregnant rat ovary

Ovarian cytosol from pseudopregnant rats was heated to 80-90 degrees C for 2 min and precipitated proteins removed by centrifugation. The supernatant of the heated ovarian cytosol contained no protein kinase C activity but when added to a control preparation containing protein kinase C, enzyme activity was increased to 200% of control. The stimulatory activity was stable to heating for 10 min, was retained on a centrifugal filtration device with a 100,000 M(r) cut-off, did not affect cAMP-dependent protein kinase, was not extractable in petroleum ether or chloroform/methanol (2:1), and enhanced the phosphorylation of protein kinase C-specific peptide substrates. The stimulatory factor was calcium-dependent and could substitute for phosphatidylserine and diacylglycerol in the protein kinase C assay. This stimulatory factor may provide a mechanism whereby the response of protein kinase C to hormonal activation could be regulated by the cell.