Reaction catalysed by glycogen phosphorylase.

A glycogen molecule with branches of only four glucose molecules ("limit-dextrin") cannot be further degraded by glycogen phosphorylase alone. It needs another enzyme:

Glycogen is degraded by the sequential action of three enzymes:

T1 - Glycogen synthesis in isolated parenchymal rat liver cells

Glycogen synthesis in the liver and muscle - Tuscany Diet

Addition of glucose-1-P to the 4' carbon of a glycogen chain is not favored thermodinamically, since the phosphate transfer potential of C-O-P bonds is quite low. Glucose-1-P will therefore be activated,i.e., transformed into a species with high phosphate transfer potential. accomplished by reaction with uridine triphosphate(UTP, an analog of ATP, with uridine replacing adenine).

Glycogen Synthesis and Metabolism

Glycogenin, which I mentioned previously, primes glycogen synthesis. The amount of glycogenin will influence how much glycogen a cell can store . Thus the production of active glycogenin primer in the cell has the potential to be the overall rate limiting process in glycogen formation. A company called markets glycogenin but not for human consumption. I don't believe that the FDA has approved synthetic glycogenin for human consumption. Another component of glycogen metabolism has been discovered which may even have greater influence on total glycogen stores than does glycogenin. This is the low molecular mass form of glycogen called proglycogen . If proglycogen could be converted into macroglycogen , muscle glycogen levels may increase significantly. I believe that this will be the next big step in glycogen resynthesis advancements.

Key hormones in the overall regulation of glycogen homeostasis include insulin, glucagon, and epinephrine.
T1 - Brain insulin action augments hepatic glycogen synthesis without suppressing glucose production or gluconeogenesis in dogs

In the synthesis of glycogen, ..

AB - In rodents, acute brain insulin action reduces blood glucose levels by suppressing the expression of enzymes in the hepatic gluconeogenic pathway, thereby reducing gluconeogenesis and endogenous glucose production (EGP). Whether a similar mechanism is functional in large animals, including humans, is unknown. Here, we demonstrated that in canines, physiologic brain hyperinsulinemia brought about by infusion of insulin into the head arteries (during a pancreatic clamp to maintain basal hepatic insulin and glucagon levels) activated hypothalamic Akt, altered STAT3 signaling in the liver, and suppressed hepatic gluconeogenic gene expression without altering EGP or gluconeogenesis. Rather, brain hyperinsulinemia slowly caused a modest reduction in net hepatic glucose output (NHGO) that was attributable to increased net hepatic glucose uptake and glycogen synthesis. This was associated with decreased levels of glycogen synthase kinase 3β(GSK3β) protein and mRNA and with decreased glycogen synthase phosphorylation, changes that were blocked by hypothalamic PI3K inhibition. Therefore, we conclude that the canine brain senses physiologic elevations in plasma insulin, and that this in turn regulates genetic events in the liver. In the context of basal insulin and glucagon levels at the liver, this input augments hepatic glucose uptake and glycogen synthesis, reducing NHGO without altering EGP.

Johnson LN (1992) Glycogen phosphorylase: control by phosphorylation and allosteric effectors. FASEB Journal 6: 2274–2282.

Glycogen Biosynthesis; Glycogen Breakdown - Oregon …

In rodents, acute brain insulin action reduces blood glucose levels by suppressing the expression of enzymes in the hepatic gluconeogenic pathway, thereby reducing gluconeogenesis and endogenous glucose production (EGP). Whether a similar mechanism is functional in large animals, including humans, is unknown. Here, we demonstrated that in canines, physiologic brain hyperinsulinemia brought about by infusion of insulin into the head arteries (during a pancreatic clamp to maintain basal hepatic insulin and glucagon levels) activated hypothalamic Akt, altered STAT3 signaling in the liver, and suppressed hepatic gluconeogenic gene expression without altering EGP or gluconeogenesis. Rather, brain hyperinsulinemia slowly caused a modest reduction in net hepatic glucose output (NHGO) that was attributable to increased net hepatic glucose uptake and glycogen synthesis. This was associated with decreased levels of glycogen synthase kinase 3β(GSK3β) protein and mRNA and with decreased glycogen synthase phosphorylation, changes that were blocked by hypothalamic PI3K inhibition. Therefore, we conclude that the canine brain senses physiologic elevations in plasma insulin, and that this in turn regulates genetic events in the liver. In the context of basal insulin and glucagon levels at the liver, this input augments hepatic glucose uptake and glycogen synthesis, reducing NHGO without altering EGP.

In the liver, glycogen synthesis and degradation are regulated to maintain blood-glucose ..

the cell has a separate mechanism for glycogen synthesis ..

Zieve FJ and Glinsmann WH (1973) Activation of glycogen synthetase and inactivation of phosphorylase kinase by the same phosphoprotein phosphatase. Biochemical and Biophysical Research Communications 50(3): 872–878.