Malantide is a synthetic dodecapeptide derived from the site phosphorylated by cAMP-dependent protein kinase (PKA) on the β-subunit of phosphorylase kinase. Malantide is a highly specific substrate for PKA with a Km of 15 μM and shows protein inhibitor (PKI) inhibition >90% substrate phosphorylation in various rat tissue extracts. Malantide is also an efficient substrate for PKC with a Km of 16 μM.