Properties of skeletal muscle phosphorylase-protein complexes

Frontal gel filtration studies on muscle extract and mixture of purified enzymes have verified the existence of a protein-complex between phosphorylase (alpha-1,4-glucan: orthophosphate glycosyltransferase EC 2.4.1.1.) and phosphorylase kinase. The complex has an apparent molecular weight of 750 000 daltons. The complex formation depends on the protein concentration and the presence of Ca2+. Removal of Ca2+ with EGTA results in the dissociation of the complex. A regulatory role may be attributed to Ca2+ since the concentration of free Ca2+ changes in skeletal muscle through the effect of hormonal or electrical stimulation. Strong association was also detected between phosphorylase kinase and phosphorylase phosphatase. The transient inhibition of phosphorylase phosphatase can be explained by this interaction.