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