[Changes in the cAMP-dependent phosphorylation system of myocardial sarcoplasmic reticulum components during...

The dissociation of the holoenzyme of the cAMP-dependent protein kinase was induced by the adrenaline-stimulated endogenous cAMP synthesis. This dissociation was impaired in a hypoxic muscle. The elevated proteolytic activity in the hypoxic area was found to be associated with the reduction of the 33P incorporation into phospholamban in the presence of 10(-6) M cAMP. No changes were observed when protein kinase was added to the incubation mixture. A correlation between the degree of phospholamban phosphorylation and its susceptibility to proteolysis was demonstrated.