This peptide is a specific substrate of PKA catalytic subunit and is phosphorylated by PKA. It contains P-2 and P-6 arginines that can be used to assess the roles of Tyr-204 and Glu-203. The peptide has a structure similar to a typical Arg-X-X-Arg-Arg-X-Ser-X phosphorylation site sequence found in substrates of cAMP dependent protein kinase. Synonym: PKA Substrate, Catalytic Subunit