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[Biochemistry](https://durgical.com/en/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.

**EC number**
[2.4.1.11](https://www.enzyme-database.org/query.php?ec=2.4.1.11)

**Genes**
GYS1, GYS2

**Structure (PDB)**
[7Q13](https://www.rcsb.org/structure/7Q13)

## 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

- [Glycogen metabolism](https://durgical.com/en/biochemistry/pathways/glycogen-metabolism/)

## Related conditions

- [Type 2 diabetes mellitus](https://durgical.com/en/conditions/type-2-diabetes-mellitus/)
- [Andersen disease (glycogen storage disease type IV)](https://durgical.com/en/conditions/andersen-disease/)
- [Pompe disease (glycogen storage disease type II)](https://durgical.com/en/conditions/pompe-disease/)

## Related

- [UDP-glucose](https://durgical.com/en/biochemistry/molecules/udp-glucose/)
- [Glycogen](https://durgical.com/en/biochemistry/molecules/glycogen/)
- [Glycogen phosphorylase](https://durgical.com/en/biochemistry/enzymes/glycogen-phosphorylase/)
- [Glucose 6-phosphate](https://durgical.com/en/biochemistry/molecules/glucose-6-phosphate/)

## 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.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: [GYS1: Glycogen [starch] synthase, muscle (human)](https://www.uniprot.org/uniprotkb/P13807/entry) (UniProt, 2026); [GYS2: Glycogen [starch] synthase, liver (human)](https://www.uniprot.org/uniprotkb/P54840/entry) (UniProt, 2026); [GYS2 gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/gys2/) (MedlinePlus, US National Library of Medicine, 2026); [7Q13: Human GYS1-GYG1 complex activated state bound to glucose-6-phosphate, uridine diphosphate, and glucose](https://www.rcsb.org/structure/7Q13) (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.

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Source: https://durgical.com/en/biochemistry/enzymes/glycogen-synthase/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/enzymes/glycogen-synthase/