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

# Catalase

Catalase breaks hydrogen peroxide down into water and oxygen; it works mainly in peroxisomes and in red blood cells.

Updated 2026-11-01

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## Key facts

- 2 H₂O₂ → 2 H₂O + O₂, with a heme (iron) in the active site.
- It lives in peroxisomes, where β-oxidation of very-long-chain fatty acids produces H₂O₂.
- It is a tetramer; each subunit has a heme and binds NADPH, which protects it from inactivation.
- It works best when H₂O₂ is high; at low levels, glutathione peroxidase is more efficient.

**EC number**
[1.11.1.6](https://www.enzyme-database.org/query.php?ec=1.11.1.6)

**Genes**
CAT

**Structure (PDB)**
[1DGH](https://www.rcsb.org/structure/1DGH)

## Regulation

- Its expression rises with oxidative stress.
- Bound NADPH prevents excess H₂O₂ from inactivating it.

## Inhibitors and toxins

- 3-Amino-1,2,4-triazole (aminotriazole)
- Cyanide and azide (bind the heme)

## Clinical notes

- Acatalasemia (CAT variants) usually causes no symptoms; some people have mouth ulcers.
- Catalase-positive microbes (Staphylococcus, Aspergillus, Candida, Nocardia) mainly harm patients with chronic granulomatous disease.
- The catalase test with hydrogen peroxide separates staphylococci (they bubble) from streptococci in the laboratory.

## Related

- [Superoxide dismutase (SOD)](https://durgical.com/en/biochemistry/enzymes/superoxide-dismutase/)
- [Glutathione peroxidase (GPX)](https://durgical.com/en/biochemistry/enzymes/glutathione-peroxidase/)
- [Reactive oxygen species and antioxidants](https://durgical.com/en/biochemistry/topics/reactive-oxygen-species-and-antioxidants/)
- [Hemoglobin and 2,3-BPG](https://durgical.com/en/biochemistry/enzymes/hemoglobin-and-2-3-bpg/)

## Test yourself

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

## What reaction does catalase catalyse?

It breaks 2 H₂O₂ into 2 H₂O and O₂ using a heme in the active site.

## In which organelle is catalase abundant?

The peroxisome, where β-oxidation of very-long-chain fatty acids makes H₂O₂.

## Why do catalase-positive microbes affect people with chronic granulomatous disease?

Their phagocytes make no superoxide and rely on microbial H₂O₂; catalase-positive microbes destroy it and survive.

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

Sources: [CAT: Catalase (human)](https://www.uniprot.org/uniprotkb/P04040/entry) (UniProt, 2026); [CAT gene: MedlinePlus Genetics](https://medlineplus.gov/genetics/gene/cat/) (MedlinePlus, US National Library of Medicine, 2026); [Acatalasemia: MedlinePlus Genetics](https://medlineplus.gov/genetics/condition/acatalasemia/) (MedlinePlus, US National Library of Medicine, 2026); [1DGH: HUMAN ERYTHROCYTE CATALASE 3-AMINO-1,2,4-TRIAZOLE COMPLEX](https://www.rcsb.org/structure/1DGH) (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.

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