Identification of a Calmodulin-Dependent Protein Kinase in the Cardiac Cytosol, which Phosphorylates Phospholamban in the Sarcoplasmic Reticulum

Abstract

A multifunctional calmodulin-dependent protein kinase in the canine cardiac cytosol was purified to near homogeneity. The purified enzyme inactivated glycogen synthase by means of phosphorylation. The enzyme also phosphorylated phospho-lamban and several other proteins. In view of its physicochemical properties and substrate specificity, the enzyme differed from myosin light chain kinase and phosphorylase kinase, and was considered to belong to a class of similar calmodulin-dependent protein kinases from brain, liver, and skeletal muscle. The results suggest that the enzyme mediates multiple Ca²⁺-dependent functions in the heart.