Autophosphorylation of adenosine 3′,5′-monophosphate-dependent protein kinase from bovine brain

A highly purified adenosine 3′,5′-monophosphate-dependent protein kinase from bovine brain has been found to catalyze its own phosphorylation. The incorporated phosphate was shown to be associated with the cyclic AMP-binding subunit (R-protein) of the protein kinase. The catalytic subunit exhibited no detectable incorporation of phosphate into itself, but was required for the phosphorylation of R-protein. The molecular weight of R-protein was determined by polyacrylamide gel electrophoresis to be about 48,000 in the presence of sodium dodecyl sulfate. Cyclic AMP strikingly inhibited the rate of autophosphorylation observed in the presence of ZnCl2, CaCl2, NiCl2, or FeCl2, but had no significant effect in the presence of MgCl2 or CoCl2. The concentration of cyclic AMP required to give half-maximal inhibition of phosphorylation was 3 × 10−7m in the presence of either CaCl2 or ZnCl2. Guanosine 3′,5′-monophosphate was far less effective under the same experimental conditions than cyclic AMP. R-protein appears to be similar to a phosphoprotein recently discovered in synaptic membrane fractions from rat and bovine cerebral cortex.