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[Biochemistry](https://durgical.com/en/biochemistry/) · Enzyme

# Galactocerebrosidase (GALC)

Galactocerebrosidase breaks down galactosylceramide and the toxic psychosine in lysosomes. Its deficiency kills myelin-forming cells: Krabbe disease.

Updated 2026-11-01

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## Key facts

- It cuts the galactose off galactosylceramide, the main glycolipid of myelin, and off psychosine (galactosylsphingosine); saposin A helps it reach the lipid.
- GALC gene (chromosome 14), autosomal recessive; more than 200 variants cause Krabbe disease, the commonest in people of European ancestry being a 30-kb deletion.
- Psychosine is the real culprit: it barely exists in healthy tissue, but piles up when GALC fails and kills oligodendrocytes and Schwann cells.
- No human crystal structure has been published: the 3D model is mouse GALC holding galactose, the reaction product, in its active site (PDB 4CCE).

**Also called**
GALC, Galactosylceramidase, Galactosylceramide β-galactosidase

**EC number**
[3.2.1.46](https://www.enzyme-database.org/query.php?ec=3.2.1.46)

**Genes**
GALC

**Structure (PDB)**
[4CCE](https://www.rcsb.org/structure/4CCE)

## Regulation

- Its natural activity is very low, which makes the enzyme assay demanding.
- Works at acid pH; reaches the lysosome tagged with mannose 6-phosphate.

## Inhibitors and toxins

- Galacto-configured iminosugars (for example galacto-isofagomine, seen bound in PDB 4UFH) studied in the laboratory as possible chaperones

## Clinical notes

- Infantile Krabbe disease: irritability, stiffness, feeding problems and seizures in the first months, with fast loss of skills.
- Some newborn screening programmes measure GALC activity and psychosine in dried blood spots, because transplant helps only if done before symptoms.
- Late-onset forms cause gait problems, spasticity and vision loss in children or adults.

## Pathways

- [Lysosomal ganglioside breakdown](https://durgical.com/en/biochemistry/pathways/lysosomal-ganglioside-breakdown/)

## Related conditions

- [Krabbe disease (globoid cell leukodystrophy)](https://durgical.com/en/conditions/krabbe-disease/)

## Related

- [Galactosylceramide (galactocerebroside)](https://durgical.com/en/biochemistry/molecules/galactosylceramide/)
- [Sulfatide](https://durgical.com/en/biochemistry/molecules/sulfatide/)
- [Sphingolipids and sphingolipidoses](https://durgical.com/en/biochemistry/topics/sphingolipids-and-sphingolipidoses/)
- [Ceramide](https://durgical.com/en/biochemistry/molecules/ceramide/)
- [Sphingosine](https://durgical.com/en/biochemistry/molecules/sphingosine/)
- [Galactose](https://durgical.com/en/biochemistry/molecules/galactose/)
- [Lysosomal storage diseases](https://durgical.com/en/biochemistry/topics/lysosomal-storage-diseases/)
- [Arylsulfatase A (ARSA)](https://durgical.com/en/biochemistry/enzymes/arylsulfatase-a/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which two substrates does galactocerebrosidase break down?

Galactosylceramide, a major myelin lipid, and psychosine (galactosylsphingosine), which is toxic to myelin-forming cells.

## Why does psychosine matter more than galactosylceramide in Krabbe disease?

Psychosine has no other route of breakdown, so it builds up and kills oligodendrocytes and Schwann cells, causing rapid demyelination.

## Why is the 3D model of galactocerebrosidase a mouse protein?

No human crystal structure has been published; the mouse enzyme is very similar and was solved with galactose in the active site.

## Why is early detection key in Krabbe disease?

Stem cell transplant can slow the disease only when done before symptoms, which is why some programmes screen newborns.

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

Sources: [GALC: Galactocerebrosidase (human)](https://www.uniprot.org/uniprotkb/P54803/entry) (UniProt, 2026); [GALC gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/galc/) (MedlinePlus, US National Library of Medicine, 2026); [Krabbe disease: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/krabbe-disease/) (MedlinePlus, US National Library of Medicine, 2026); [RCSB PDB - 4CCE: STRUCTURE OF MOUSE GALACTOCEREBROSIDASE WITH GALACTOSE: ENZYME- PRODUCT COMPLEX](https://www.rcsb.org/structure/4CCE) (RCSB Protein Data Bank, 2026); [Glycosphingolipid catabolism](https://reactome.org/PathwayBrowser/#/R-HSA-9840310) (Reactome, 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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