Evidence for phosphorylation of rat brain guanylate cyclase by cyclic AMP-dependent protein kinase

Direct phosphorylation of purified rat brain guanylate cyclase by cyclic AMP-dependent protein kinase is demonstrated. In the presence of γ-³²P]ATP, ³²P was incorporated into the protein to the extent of 0.8 to 0.9 mol/mol of guanylate cyclase. The presence of ³²P in the guanylate cyclase molecule was demonstrated by gel-filtration and by autoradiography after gel electrophoresis. The phosphorylation was accompanied by an increase in enzyme activity, characterized by an increase of V_M. These results suggest that the activity of guanylate cyclase may be regulated in vivo by phosphorylation.