Phosphorylation and activation of the cardiac isoenzyme of phosphorylase kinase by the cAMP-dependent protein kinase.
The cAMP-dependent protein kinase catalyzes the phosphorylation of the alpha- and beta-subunits of the cardiac isozyme of phosphorylase kinase. beta-Subunit phosphorylation achieves a maximum level of between 1 to 2 mol of phosphate/mol of phosphorylase kinase, a value less than the stoichiometric content of beta-subunits in the enzyme. This, less than stoichiometric incorporation, is not a result of the presence of endogenous phosphate in equivalent sites in the remaining beta-subunit moieties. Pretreatment of phosphorylase kinase with phosphoprotein phosphatase, under conditions proven to dephosphorylate such sites, does not modify the observed extent of beta-subunit phosphorylation. alpha'-Subunit phosphorylation is initiated at a slower rate than beta but achieves a higher maximum level of incorporation. alpha'-Subunit phosphorylation, but not the extent of beta-subunit phosphorylation, is stimulated by MnCl2 and partially inhibited by NaF; neither is effected by ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid. The activation of cardiac phosphorylase kinase that occurs concomitantly with phosphorylation appears to be dependent upon phosphate incorporation into both the alpha- and beta-subunits. At low levels of activation a close correlation is observed between activation and either alpha-subunit phosphorylation, beta-subunit phosphorylation, or total phosphorylation. However, the cAMP-dependent catalyzed phosphorylation of alpha, at a time after which beta-subunit phosphorylation is already maximal, also results in activation of cardiac phosphorylase kinase.
D000818:Animals; D002417:Cattle; D000242:Cyclic AMP / Q000494:pharmacology; D004789:Enzyme Activation; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D009206:Myocardium / Q000201:enzymology*; D010764:Phosphorylase Kinase / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*
D007527:Isoenzymes; D046911:Macromolecular Substances; D008345:Manganese; D000242:Cyclic AMP; D011494:Protein Kinases; D010764:Phosphorylase Kinase; D008274:Magnesium