This peptide is a synthetic substrate for protein kinase A (PKA) with a Km = 3.9 uM. The peptide sequence corresponds to residues 123-135 of human cAMP-response element-binding protein (CREB) and contains the Ser-133 phosphorylation site for CaMK1, CaMK2 and CaMK4.H-Lys-Arg-Arg-Glu-Ile-Leu-Ser-Arg-Arg-Pro-Ser-Tyr-Arg or H-KRREILSRRPSYR