Glycogen m

Notes

•Glycogen Metabolism Regulation Glycogen metabolism is controlled by hormonal and allosteric mechanisms to maintain energy balance at both cellular and whole-body levels. Two main enzymes govern this process: glycogen synthase, which promotes glycogen synthesis, and glycogen phosphorylase, which facilitates glycogen breakdown. These enzymes are reciprocally regulated, preventing simultaneous activation of synthesis and degradation. •Fed State Regulation In the fed state, elevated blood glucose triggers insulin release. Insulin binds to its receptor tyrosine kinase (RTK) on the cell membrane, activating the PI3K–Akt pathway. Akt activation stimulates protein phosphatase-1 (PP1), which dephosphorylates target enzymes. PP1 activates glycogen synthase by dephosphorylation, promoting glycogen synthesis. Concurrently, PP1 dephosphorylates and inactivates glycogen phosphorylase and phosphorylase kinase, inhibiting glycogen breakdown and favoring storage. •Fasting State Regulation During fasting, glucagon primarily acts in the liver. It binds to Gs protein-coupled receptors, increasing intracellular cAMP levels. Elevated cAMP activates protein kinase A (PKA), which phosphorylates a...