Cyclic AMP-dependent protein kinase and Ca2+-calmodulin stimulate the formation of polyphosphoinositjdes in a sarcoplasmic reticulum preparation of rabbit heart

AbstractA rabbit heart membrane fraction enriched in sarcoplasmic reticulum was incubated in a reaction mixture containing [γ-32P]ATP. The catalytic subunit of cyclic AMP-dependent protein kinase enhanced the 32P-labelling of both phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate. Ca2+-calmodulin also increased the 32P-incorporation into both polyphosphoinositides. Upon SDS gel-electrophoretic analysis of the membrane proteins, phospholamban was found to be concurrently phosphorylated by the exogenous catalytic subunit as well as by an endogenous Ca2+-calmodulm-dependent protein kinase