EXOGENOUS SUBSTRATE STIMULATES AUTODEPHOSPHORYLATION OF CYCLIC-AMP-DEPENDENT PROTEIN KINASE-II

The autophosphorylated regulatory subunit (P-32-RII) of cyclic-AMP-dep endent protein kinase II was efficiently dephosphorylated by its C sub unit in the absence of added ADP, provided that Mg/ATP and a standard protein kinase peptide substrate were present. This raises the possibi lity that autodephosphorylation could be significant in the intact cel l. Only the cyclic-AMP-complexed free form of P-32-RII was efficiently dephosphorylated, indicating that the autodephosphorylation was inter molecular. Autodephosphorylation of P-32-RII in the presence of MgATP and kemptide occurred with formation of [gamma-P-32]ATP, suggesting tr ansfer of P-32 of phospho-RII to a transient C(MgADP) complex formed during the forward kinase reaction with peptide as substrate. Autodeph osphorylation promoted by phosphorylation of exogenous substrates coul d operate also for other kinases conforming to a mechanism where MgADP remains bound to the active site after the other product (phosphoryla ted substrate) has left the catalytic complex.