Cardiac phosphorylase kinase. Deactivation by selective dephosphorylation of alpha' and beta subunits

We have documented previously that although the phosphorylation of the beta subunit of cardiac phosphorylase kinase plays a major role in activation of the enzyme, enzyme activity is also modulated by either cAMP-dependent or cAMP-independent phosphorylation of the alpha' subunit (Sul, H. S., Cooper R. H., Whitehouse S., and Walsh D. A. (1982) J. Biol. Chem. 257, 3484-3490). This paper reports that deactivation of 32P-labeled cardiac phosphorylase kinase by protein phosphatase occurs concomitantly with the dephosphorylation of either the alpha' or beta subunits. However, enzyme activation attributable to alpha' subunit phosphorylation is still apparent after dephosphorylation of the beta subunit and, similarly, that caused by beta subunit phosphorylation is maintained after alpha' subunit dephosphorylation. These data support out previously stated conclusion that both alpha' and beta subunit phosphorylation regulates the activity of cardiac phosphorylase kinase.