HIGH-MOLECULAR-WEIGHT CALMODULIN-BINDING PROTEIN IS PHOSPHORYLATED BYCALMODULIN-DEPENDENT PROTEIN-KINASE-VI FROM BOVINE CARDIAC-MUSCLE

A high molecular weight calmodulin-binding protein (HMW CaMBP) from bo vine heart cytosolic fraction was purified to apparent homogeneity. A novel CaM-dependent protein kinase was originally discovered when the total CaM-binding protein fraction from cardiac muscle was loaded on a gel filtration column, The CaM-dependent protein kinase was shown by gel filtration chromatography to have an apparent molecular mass of 36 ,000 daltons. The CaM-dependent protein kinase has been highly purifie d by sequential chromatography on DEAE-Sepharose Cl 6B (to remove calm odulin), CaM-Sepharose 4B, phosphocellulose, Sepharose 6B gel filtrati on and Mono S column chromatographies. The highly purified protein kin ase stoichiometrically phosphorylated the HMW CaMBP in a Ca2+/CaM-depe ndent manner. The phosphorylation resulted in the maximal incorporatio n of 1 mol of phosphate/mol of the HMW CaMBP. The distinct substrate s pecificity of this protein kinase indicates that it is not related to the known protein kinases (I, II, III, IV and V) that have been alread y characterized, therefore we would like to designate this novel kinas e as a CaM-dependent protein kinase VI.