The studies proposed in this application have as a long term objective the determination of the role of protein kinases in regulating glycogen synthase. We propose to purify to homogeneity a cyclic AMP-independent and calcium-independent glycogen synthase kinase from muscle and to study its properties. In addition, we plan to examine the role of glycogen synthase kinases in mediating the effects of insulin and diabetes on glycogen synthase activity. In some cases kinase assays will be conducted under conditions which mimic intracellular conditions, since changes in kinase activity may be more readily detected in this way. We will incubate isolated rat soleus muscle with 32Pi in the presence and absence of insulin to measure changes in phosphorylation of glycogen synthase and regulatory subunit of cyclic AMP-dependent protein kinase. The 32p-labeled glycogen synthase will be subjected to peptide mapping to determine which of the several phosphorylation sites in this enzyme are altered by insulin treatment. We will add preparations of kinases to the phospho form of glycogen synthase isolated from normal rat muscle in order to determine if a given kinase can mimic the activity and phosphorylation changes produced by insulin dificiency. These studies should lead to a better understanding of how insulin regulates glycogen synthesis in skeletal muscle.
