ABSTRACT
This chapter summarizes the findings concerning the substrate specificity of cyclic guanosine 3',5'-monophosphate (cGMP) dependent protein kinase and compares this specificity to that of the cyclic adenosine 3',5'-monophosphate (cAMP) dependent enzyme. The cGMP-dependent and cAMP dependent protein kinases have each been purified to homogeneity, and their physicochemical properties and subunit structures are well characterized. The ammo-terminal half of each subunit of cGMP-dependent protein kinase contains the regulatory domain that is homologous to the regulatory subunits of the cAMP-dependent enzyme. The catalytic domain of cGMP-dependent protein kinase is comprised of residues 341 through the carboxy-terminus. This catalytic domain is homologous to the free catalytic subunit of the cAMP-dependent protein kinase. One protein of known primary structure which is a substrate for phosphorylation by the cGMP-dependent protein kinase is the enzyme itself. The cGMP-dependent protein kinase undergoes autophosphorylation in the absence of bound cyclic nucleotide or in the presence of either cGMP or cAMP.
