Effect of protein kinase modulator on cAMP-dependent protein kinase-catalyzed phosphorylation of phospholamban and stimulation of calcium transport in cardiac sarcoplasmic reticulum.
The heat-stable protein (protein kinase modulator), partially purified from fresh bovine heart, possessed the ability to inhibit and stimulate adenosine 3':5'-monophosphate (cAMP)-dependent protein kinase and guanosine 3':5'-monophosphate (cGMP)-dependent protein kinase activities, respectively. The inhibitory activity of protein kinase modulator on cAMP-dependent protein kinase was abolished almost completely by trypsin treatment, while the ability to stimulate cGMP-dependent protein kinase activity was resistant to trypsin. Fractionation by a linear potassium phosphate gradient on DEAE-cellulose column did not clearly separate both activities. Phosphorylation of cardiac microsomal component, "phospholamban" (molecular weight = 22,000), was inhibited almost completely by the saturating amounts of protein kinase modulator. This inhibition of phospholamban phosphorylation by protein kinase modulator was accompanied by a decreased Ca uptake rate that had been stimulated by cAMP-dependent protein kinase. These findings indicate that protein kinase modulator is functional in controlling the cAMP-dependent protein kinase-catalyzed phosphorylation of phospholamban and the rate of calcium transport, lending further support for the previously proposed mechanism, in which phospholamban is assumed to serve as a regulator of calcium transport in cardiac sarcoplasmic reticulum.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D000242:Cyclic AMP / Q000494:pharmacology*; D004285:Dogs; D004789:Enzyme Activation; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D008861:Microsomes / Q000378:metabolism; D009124:Muscle Proteins / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D000099211:Phospholamban
D002118:Calcium; D002135:Calcium-Binding Proteins; D002352:Carrier Proteins; D000242:Cyclic AMP; D009124:Muscle Proteins; D011494:Protein Kinases; D000099211:Phospholamban