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

# α-L-Iduronidase

α-L-Iduronidase removes iduronic acid from the end of dermatan and heparan sulfate in the lysosome. Its absence causes mucopolysaccharidosis I (Hurler).

Updated 2026-11-01

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## Key facts

- It hydrolyses the terminal (unsulfated) α-L-iduronic acid of dermatan sulfate and heparan sulfate.
- It acts right after iduronate 2-sulfatase (IDS gene), which first removes the sulfate; that enzyme is missing in Hunter syndrome.
- IDUA gene (4p16.3); autosomal recessive inheritance.
- Without it, both GAGs build up in lysosomes and spill into urine.

**Also called**
IDUA

**EC number**
[3.2.1.76](https://www.enzyme-database.org/query.php?ec=3.2.1.76)

**Genes**
IDUA

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

## Regulation

- Active at acid pH.
- Reaches the lysosome tagged with mannose 6-phosphate; neighbouring cells can take up the secreted enzyme (cross-correction).

## Inhibitors and toxins

- Iduronic acid analogues (laboratory iminosugars, such as the one in PDB 4KGL)

## Clinical notes

- Severe MPS I (Hurler): coarse features, corneal clouding, lumbar gibbus, hepatosplenomegaly, valve disease and cognitive decline.
- Attenuated MPS I (Hurler–Scheie, Scheie): stiff joints, corneal clouding and valve disease with normal or near-normal intelligence.
- Haematopoietic stem cell transplant before age two also delivers enzyme to the brain; intravenous replacement treats organs and joints.

## Related conditions

- [Hurler syndrome (mucopolysaccharidosis type I)](https://durgical.com/en/conditions/hurler-syndrome/)
- [Hunter syndrome (mucopolysaccharidosis type II)](https://durgical.com/en/conditions/hunter-syndrome/)

## Related

- [Glycosaminoglycans (mucopolysaccharides)](https://durgical.com/en/biochemistry/topics/glycosaminoglycans/)
- [Lysosomal storage diseases](https://durgical.com/en/biochemistry/topics/lysosomal-storage-diseases/)
- [Mannose 6-phosphate tagging (sending enzymes to the lysosome)](https://durgical.com/en/biochemistry/topics/mannose-6-phosphate-tagging/)

## Test yourself

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

## Which enzyme acts just before α-L-iduronidase in dermatan sulfate breakdown?

Iduronate 2-sulfatase, which removes the sulfate; it fails in Hunter syndrome.

## What is cross-correction?

A healthy cell secretes enzyme carrying mannose 6-phosphate and a sick cell takes it up by its receptor; this underlies transplant and replacement.

## Which GAGs build up when α-L-iduronidase is missing?

Dermatan sulfate and heparan sulfate.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/biochemistry/enzymes/l-iduronidase/)

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

Sources: [IDUA: Alpha-L-iduronidase (human)](https://www.uniprot.org/uniprotkb/P35475/entry) (UniProt, 2026); [IDUA gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/idua/) (MedlinePlus, US National Library of Medicine, 2026); [4OBR: Crystal structure of human alpha-L-iduronidase complex with alpha-L-iduronic acid](https://www.rcsb.org/structure/4OBR) (RCSB Protein Data Bank, 2026); [MPS I - Hurler syndrome (HS-GAG degradation)](https://reactome.org/PathwayBrowser/#/R-HSA-2206302) (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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Source: https://durgical.com/en/biochemistry/enzymes/l-iduronidase/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/enzymes/l-iduronidase/