phosphorylase kinase

Phosphorylase Kinase β-Subunit Fragment (420-436) is a peptide fragment (430-436) derived from the β-Subunit of phosphorylase kinase. Phosphorylase kinase, a serine/threonine-specific protein kinase, plays a crucial role in activating glycogen phosphorylase for the release of glucose-1-phosphate from glycogen [1].

The cyanobacterium Nodularia spumigena often contaminates the drinking water of rural communities in developing countries and accumulates in mussels, flounder, and cod from the northern Baltic Sea. Nodularin is a hepatotoxic monocylic pentapeptide produced by the N. spumigena. It is a potent inhibitor of protein phosphatase types 1 (PP1) and 2A (PP2A), exhibiting IC50 values of 1.8 and 0.026 nM, respectively. PP2B is inhibited to a lesser extent with an IC50 of 1.8 μM. No apparent inhibitory effect is observed with PP2C, alkaline phosphatase, acid phosphatase, insulin receptor tyrosine kinase, protein kinase A, phosphorylase kinase, or protein kinase C.

Malantide TFA, a synthetic dodecapeptide, originates from the phosphorylation site targeted by cAMP-dependent protein kinase (PKA) on the β-subunit of phosphorylase kinase. Exhibiting a high specificity for PKA with a Michaelis constant (Km) of 15 μM, this compound demonstrates more than 90% inhibition of substrate phosphorylation in the presence of protein inhibitor (PKI) across various rat tissue extracts [1]. Moreover, Malantide TFA acts as an effective substrate for Protein Kinase C (PKC) with a Km of 16 μM [2].

Myelin Basic Protein (MHP4-14) TFA, a synthetic peptide comprising residues 4-14 of myelin basic protein, serves as a highly selective substrate for protein kinase C (PKC) with a K_m of 7 μM. It is not phosphorylated by cyclic AMP-dependent protein kinase, casein kinases I and II, Ca^2+/calmodulin-dependent protein kinase II, or phosphorylase kinase, making it an ideal candidate for protein kinase C assays in crude tissue extracts, ensuring minimal background interference [1] [2].