The effect of the cAMP-dependent protein kinase on protein phosphorylation and phosphatidylinositol 4-phosphate formation in a hepatocyte membrane preparation.

Plasma membrane preparation obtained from isolated mouse hepatocytes was phosphorylated by exogenous cyclic AMP dependent protein kinase in the presence of 32P-ATP. The phosphorylated proteins were analysed by SDS-polyacrylamide gel-electrophoresis of the membrane and the phosphorylated lipids were analysed by thin layer chromatography of the separated lipid fraction. The protein kinase stimulated the 32P incorporation into phosphatidylinositol 4-phosphate and it catalyzed the phosphorylation of several proteins. The main phosphoprotein bands were found at 51 kDa, 49 kDa, 46 kDa and 34 kDa. A part of the 51 kDa phosphoprotein accompanied the lipids in the course of the separation of the lipid fraction.