Immunological Distinction Between Guanosine 3':5'-monophosphate-dependent and Adenosine 3':5'-monophosphate-dependent Protein Kinases

A guanosine 3':5'-monophosphate (cGMP)-dependent protein kinase was purified from bovine lung using 8-(6-aminohexylamino)-cAMP-Sepharose. The activity of the purified enzyme was highly dependent on cGMP using histone f2b as a substrate. The self-phosphorylation of the purified enzyme was strongly inhibited by cGMP and not significantly affected by cAMP. A precipitating antiserum prepared in rabbits against the cGMP-dependent protein kinase specifically inhibited the histone kinase activity and the self-phosphorylation of the purified cGMP-dependent protein kinase without affecting the cGMP binding site. This antiserum also specifically inhibited the phosphorylation of the endogenous substrate proteins by endogenous cGMP-dependent protein kinase in smooth muscle membranes, but did not cross-react detectably with catalytic subunit or regulatory subunit of type I or type II cAMP-dependent protein kinase. Conversely, anti-sera against the regulatory subunit of type I or type II cAMP-dependent protein kinase did not cross-react detectably with cGMP-dependent protein kinase. The substantial differences between the immunological properties of the cGMP-dependent and cAMP-dependent protein kinases suggest that these two enzymes have distinct physiological roles.