Control of Glycogen Metabolism in Human Muscle

Abstract

LITTLE is known of the mechanisms that control the resting level of glycogen in either normal or pathological human muscle. Animal studies, however, suggest that the polysaccharide itself plays a role in the regulation of its own metabolism by influencing the proportion of active and inactive forms of glycogen synthetase, the principal synthetic enzyme,¹so that increased tissue levels of glycogen retard synthesis of the polysaccharide. Glycogen inhibits the phosphatase that converts the dependent (D) form of synthetase to the presumably more active independent (I) form.²Similarly, the principal degradative enzyme, phosphorylase, exists in active and inactive forms that are also modified by glycogen. High tissue levels of the polysaccharide increase the proportion of active phosphorylase a at the expense of the inactive phosphorylase b,³primarily through effects on a separate enzyme, phosphorylase b kinase, that catalyzes the conversion of phosphorylase b to a.⁴