Cyclic AMP-dependent protein kinase stimulates the phosphorylation of phosphatidylinositol to phosphatidylinositol-4-monophosphate in a plasma membrane preparation from pig granulocytes.

Plasma membranes prepared from pig granulocytes were incubated in the presence of [gamma-32P]ATP. The dissociated catalytic subunit of cyclic AMP-dependent protein kinase stimulated the incorporation of 32P into both the protein and lipid fractions of the membrane. The SDS gel-electrophoretic analysis of the 32P-labelled proteins showed that the protein kinase phosphorylated preferentially a 24000-Mr protein, though other 32P-labelled proteins were also detected. 32P-labelled membrane lipids were analysed in two different thin layer chromatographic systems. 32P-labelling was found exclusively in polyphosphoinositides. On addition of the protein kinase the 32P-labelling of both polyphosphoinositides was increased but a higher amount of phosphate was incorporated into phosphatidylinositol-4-phosphate than into phosphatidylinositol-4,5-bisphosphate.