This chapter reviews knowledge of mammalian liver glycogen synthase and its short-term regulation by covalent phosphorylation mechanisms. Elevated concentrations of insulin and glucose promote glycogen synthesis and the activation of glycogen synthase. Liver glycogen synthesis during recovery from fasting does not involve direct conversion of glucose to glycogen but passage through 3-carbon intermediates. However, irrespective of the history of the carbons of the UDP glucose precursor, the effect of glucose to stimulate glycogen synthesis is likely to be an important regulatory interaction. Fasting rapidly depletes liver glycogen and the primary positive stimulus is glucagon. Liver glycogen can be mobilized by other hormones, such as epinephrine, vasopressin, and angiotensin II. All of these glycogenolytic hormones suppress glycogen formation by inactivating glycogen synthase. It is now clear that liver and muscle glycogen synthases, though closely related proteins, are distinct isozymes, differing in primary structure and therefore coded by separate genes.
ASJC Scopus subject areas
- Molecular Biology