Phosphorylase Kinase from Rabbit Skeletal Muscle

This chapter discusses phosphorylase kinase derived from rabbit skeletal muscle. The phosphorylation of phosphorylase takes place on a serine, 14 residues from the N-terminus of the polypeptide chain and converts the enzyme from a form that requires adenosine monophosphate (AMP) for activity to one that is almost fully active in the absence of this allosteric effector. The phosphorylation of glycogen synthase occurs on a serine only seven residues from the N- terminus and transforms the enzyme from a form that is almost fully active in the absence of glucose-6-phosphate to one that is more dependent on this activator. The phosphorylation of glycogen phosphorylase and glycogen synthase occurs at comparable rates in vitro. The conversion of phosphorylase can be conveniently followed by assaying phosphorylase in the absence of AMP.