Total conversion of glycogen synthase from the I- to the D-form by a cyclic AMP-independent protein kinase from rabbit skeletal muscle.

Abstract

A newly discovered cyclic AMP-independent protein kinase, which catalyzes the total conversion of glycogen synthase from the I-to the D-form, has been isolated from rabbit skeletal muscle.This enzyme, designated glycogen synthase kinase, is separable from cyclic AMP-dependent protein kinase by column chromatography on phosphocellulose.Synthase kinase and cyclic AMP-dependent protein kinase are distinct in their specificity for protein substrates, the effects of cyclic AMP and the inhibitor of cyclic AMPdependent protein kinase on their activities, and the extent to which they phosphorylate I-form glycogen synthase.The phosphorylation of I-form enzyme by synthase kinase results in the incorporation of 4 mol of phosphateB5,OOO subunit; however, only two of the phosphate sites seem predominantly to determine glucose-6-P dependence.The resulting multiply phosphorylated enzyme, which is highly dependent on glucose-6-P for activity, has a phosphate content comparable to the D-form enzyme isolated from rabbit muscle.