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PATHWAYS: GLYCOGEN & GLUCOSE ¹

Carbohydrate Glucose to Pyruvate   Animation Glycogenolysis Glycolysis Glycogen disorders Glycogen Synthesis Also see   Lipid metabolism

From: R Brian Sommerville

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Glycogenolysis Pathway

Glycogen: Structure regulation Laforin Regulates glucan chain length & Phosphorylation levels Glycan phosphatase Dependent on malin Lafora disease: Poorly soluble glycogen Malin E3 ubiquitin ligase Marks proteins for proteasomal degradation Ubiquitination effect: Depends on laforin Ubiquitiated proteins: GS, GDE, PP1 R5/PTG, R6 Other associated molecules Starch-binding domain-containing protein 1 (STBD1) AMP-activated protein kinase (AMPK) Phosphorylase kinase (PhK) Protein phosphatase 1 (PP1) Polyglucosan Cytoplasm Glycogen Phosphorylase (PYGM; GP) Removes glucose residues from α-(1,4)-linkages within glycogen molecules Activity of ceases 4 glucose residues away from an (1→6)-α glycosidic branch point Product of reaction: Glucose-1-phosphate Debrancher enzyme (GDE) Removes glucose from branch points (α-(1→6)-linkages) within glycogen Transferring 3 glucose residues to another non-reducing end of a glycogen chain Hydrolyzes 4th glucose residue at branch point: Releases free glucose Lysosomal: Acid α-glucosidase (GAA) Hydrolyzes α-(1→4) glycosidic bonds Releases: Glucose-1-phosphate Later steps Phosphoglucomutase Converts glucose-1-phosphate to glucose-6-phosphate Skeletal muscle: Glucose-6-phosphate is metabolized by the glycolytic pathway Diseases: CDG1t; GSD14 Phosphorylase b kinase Reactivates Phosphorylase: Via Phosphorylation Hexokinase Phosphorylates glucose Phosphorylated glucose: Enters glycolytic pathway

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Glycolysis Pathway

Also see: MedicalBiochemistry

Progressive changes Glycolysis of glucose to pyruvate. = Adenosine = Phosphate From University of Virginia

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Glycogen: Synthesis Pathway & Structure

• Synthesis: Enzyme Components
  • Glycogenin-1 (GYG): Autoglycosylation
    • Forms initial linear (1→4)-α glycosidic glucan chain: ~ 10-20 Glucose residues
  • Glycogen Synthase (GS)
    • Elongates glucan chain by adding glucose residues to non-reducing end
  • Glycogen Branching Enzyme (GBE)
    • Transfers 6-8 glucose residues from nonreducing end of glucan chain to carbon-6 atom of glucose residue in another chain
    • Creates branched (1→6)-α glycosidic linkage
• Glycogen: Structure
  • General
    • Glycogen forms: Globular & Branched
    • Optimizes: Storage & Utility
  • Covalent bonds between glucose residues
    • (1→4)-α linkages: Join glucose molecules linearly
    • (1→6)-α linkages: Introduce a tree-like branching pattern
  • Linear chains of glycogen contain
    • ~10-14 glucose units with ≤ 2 branch points
    • Branch points: Separated by ≥ 4 monomer units
  • Macromolecules (β particles)
    • Contain: 50,000 glucose residues
    • Shapes: Irregular, Globular, Diameters 20 - 40 nm
    • Core: Spherical
    • Periphery: Less dense; Dispersed branches at edges
  • α particles: Large composite molecules
    • Formed by bound aggregation of multiple β particles
    • Diameter: 200 nm in diameter
    • Structure: Rosette-like
  • Protein core
    • Contents: Glycogenin & other glycogen synthetic molecules
    • Glycogenin: May form linkage for formation of α particles
  • Phosphate
    • 1 moiety/500 to 2500 glucose units in glycogen
    • Monoesters
    • Attached to: C2, C3 and C6 hydroxyls of glucose moieties
    • Higher concentration of phosphates in glycogen inner core
    • Phosphorylation: Increases glycogen solubility

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References
1. Carbohydr Polym 2024;346:122631

9/10/2024