Malantide, Protein Kinase Substrate

Malantide, Protein Kinase Substrate is a synthetic tetradecapeptide derived from the phosphorylation site of the β-subunit of phosphorylase kinase. The compound is a highly specific substrate for PKA and has displayed PKI inhibition >90% substrate phosphorylation in various tissue extracts at a K_m=15 μM for PKA and 223 μM for PKG. Malantide is also a substrate for PKC and catalyzes the phosphorylation of serine in other substrates, including troponin I. More recently the compound has been used in studies to directly detect the phosphorylated peptides by electrospray ionization mass spectrometry; shown as a realistic alternative to radioactivity and fluorescence detection in determining enzymatic activity.