DOES PHOSPHORYLASE-KINASE CONTROL GLYCOGEN BIOSYNTHESIS IN SKELETAL-MUSCLE

Immunoblotting as well as enzyme assays demonstrate the presence of th e self-glucosylating protein, glycogenin, in the protein-glycogen comp lex, in the sarcoplasmic reticulum and in phosphorylase kinase. In all three compartments glycogenin occurs in different, albeit, defined gl ucosylated forms, which upon deglucosylation are converted into a 42 k Da form. We suggest that phosphorylase kinase might have a dual functi on in glycogen biogenesis: firstly, control of glycogen degradation in the protein-glycogen complex via phosphorylation of glycogen phosphor ylase b; secondly, regulation of glycogen biosynthesis on the sarcopla smic reticular membranes via phosphorylation and thereby inhibition of glycogen synthase.