Identification of a calmodulin-dependent glycogen synthase kinase in rabbit skeletal muscle, distinct from phosphorylase kinase

A glycogen synthase kinase that is completely dependent on Ca²⁺ and calmodulin has been identified in mammalian skeletal muscle, and purified ∼3000-fold by chromatography on phosphocellulose and calmodulin-Sepharose. The presence of 50 mM NaCl in the homogenisation buffer was critical for extraction of the enzyme. The calmodulin-dependent glycogen synthase kinase (app. M_r 850 000) is distinct from myosin light-chain kinase and phosphorylase kinase, but phosphorylates the same serine residue on glycogen synthase as phosphorylase kinase. The physiological role of the enzyme is discussed.