Biochemistry · Enzyme
Glycogen synthase !
Glycogen synthase lengthens glycogen chains with glucose taken from UDP-glucose; insulin activates it after a meal.
Updated 2026-11-01
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Key facts
- UDP-glucose + glycogen (n) → glycogen (n + 1) + UDP, with α-1,4 bonds.
- It is the regulated enzyme of synthesis: dephosphorylated it is active (form a) and phosphorylated inactive (form b).
- It cannot start from scratch: it needs glycogenin as a primer.
- Structure 7Q13 is the human GYS1–glycogenin complex with glucose 6-phosphate (activator) and UDP in the active site.
Regulation
- Insulin: inhibits GSK-3 (via Akt) and activates protein phosphatase 1 → synthase dephosphorylated and active.
- Glucagon and adrenaline: PKA, GSK-3 and other kinases phosphorylate and inactivate it.
- Glucose 6-phosphate activates it allosterically even when phosphorylated.
Inhibitors and toxins
- Phosphorylation by GSK-3 and PKA (physiological)
- GYS1 inhibitors under study for Pompe disease and other glycogen storage diseases
Clinical notes
- GYS2 deficiency (GSD 0) causes fasting hypoglycaemia and ketosis, with high glucose and lactate after meals.
- In insulin resistance muscle stores less glucose as glycogen.
Pathways
Related conditions
- Type 2 diabetes mellitus
- Andersen disease (glycogen storage disease type IV)
- Pompe disease (glycogen storage disease type II)
Related
Test yourself
Think of the answer, then tap the question to see it.
Is glycogen synthase active when phosphorylated or dephosphorylated?
Dephosphorylated; insulin activates phosphatase 1, which removes the phosphates.
Which bond does glycogen synthase make?
The α-1,4 bond between glucose units; the α-1,6 branches are made by the branching enzyme.
Which allosteric activator stimulates glycogen synthase?
Glucose 6-phosphate, which signals spare glucose.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: GYS1: Glycogen [starch] synthase, muscle (human) (UniProt, 2026); GYS2: Glycogen [starch] synthase, liver (human) (UniProt, 2026); GYS2 gene: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026); 7Q13: Human GYS1-GYG1 complex activated state bound to glucose-6-phosphate, uridine diphosphate, and glucose (RCSB Protein Data Bank, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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Representative model, for educational purposes only.