using subunit specific protein phosphatases ( the polycation-stimulated and atp- , mg2+-dependent enzymes ) , we show that the degree of phosphorylation of both the alpha and beta subunits modulates phosphorylase kinase activity . beta subunit phosphorylation is essential for activation and , independent of the degree of alpha subunit phosphorylation , enzyme fully dephosphorylated in the beta subunit is completely inactivated . alpha subunit phosphorylation does , however , also regulate activity , and enzyme fully or partially phosphorylated in the beta subunit is inactivated as a consequence of alpha subunit dephosphorylation .
C0031686
protein phosphatases
C1158884
dephosphorylation