Amino acid sequence of the regulatory subunit of bovine type II cAMP-dependent protein kinase

Evidence is presented that establishes the amino acid sequence of the regulatory subunit of type II cAMP-dependent protein kinase from bovine cardiac muscle. Complementary sets of overlapping peptides were generated primarily by tryptic digestion and by chemical cleavage at methionyl residues. The analysis was augmented by chemical cleavage at a single tryptophanyl residue and at three of the four aspartyl-proline bonds. Several large fragments generated by limited proteolysis contributed to the proof of structure. The subunit is a single chain of 400 residues corresponding to a molecular weight of 45 004. An amino-terminal segment of about 100 residues is believed to include the region responsible for oligomeric association. The remainder of the molecule consists of two tandem homologous domains, each of which is thought to bind a single molecule of cAMP. Comparison of the three domains with corresponding regions of the type I isozyme, of the Escherichia coli catabolite gene activator protein, and of cGMP-dependent protein kinase indicates extensive regions of homology and as much as 50% identity with the sequence of an internal segment of the type I isozyme.