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# Peroxisomal oxidation (β- and α-oxidation)

The peroxisome shortens very-long-chain fatty acids and breaks down phytanic acid, which mitochondria cannot process.

Updated 2026-11-01

## Key facts

- Very-long-chain fatty acids (22 C or more) enter the peroxisome through the ABCD1 transporter and are shortened there.
- First step by acyl-CoA oxidase: electrons go straight to O₂ forming H₂O₂ (removed by catalase), with no ATP.
- Phytanic acid (branched, from dairy and ruminant meat) needs α-oxidation: it loses one carbon and then follows β-oxidation.
- The peroxisome also makes plasmalogens and bile acids.

## In detail

- 1. ABCD1 (ALDP) imports very-long-chain acyl-CoAs into the peroxisome.
- 2. Acyl-CoA oxidase 1 forms the double bond and passes electrons to O₂: H₂O₂ instead of FADH₂.
- 3. The bifunctional protein (HSD17B4) hydrates and oxidises; thiolase cuts off acetyl-CoA.
- 4. When the chain reaches about 8 C, it leaves as acylcarnitine for the mitochondrion to finish.
- 5. Phytanic acid: phytanoyl-CoA hydroxylase (PHYH) starts α-oxidation and gives pristanate, which follows peroxisomal β-oxidation.

**Also called**
Peroxisomal β-oxidation, Phytanic acid α-oxidation

## Clinical notes

- Zellweger: functional peroxisomes are missing; very-long-chain, phytanic and pristanic acids build up and plasmalogens are lacking.
- X-linked adrenoleukodystrophy: ABCD1 fails; very-long-chain fatty acids build up in white matter and adrenal glands.
- Refsum disease: PHYH fails; phytanic acid builds up and damages retina, nerves and hearing.

## Pathways

- [Fatty acid β-oxidation](https://durgical.com/en/biochemistry/pathways/fatty-acid-oxidation/)

## Related conditions

- [Zellweger syndrome (Zellweger spectrum)](https://durgical.com/en/conditions/zellweger-syndrome/)
- [Refsum disease (adult)](https://durgical.com/en/conditions/refsum-disease/)
- [X-linked adrenoleukodystrophy](https://durgical.com/en/conditions/x-linked-adrenoleukodystrophy/)

## Related

- [Fatty acid β-oxidation](https://durgical.com/en/biochemistry/pathways/fatty-acid-oxidation/)
- [Acetyl-CoA](https://durgical.com/en/biochemistry/molecules/acetyl-coa/)
- [Carnitine (L-carnitine)](https://durgical.com/en/biochemistry/molecules/carnitine/)
- [Palmitate (palmitic acid)](https://durgical.com/en/biochemistry/molecules/palmitate/)

## Test yourself

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

## What does the first step of peroxisomal β-oxidation produce instead of FADH₂?

Hydrogen peroxide (H₂O₂), because acyl-CoA oxidase hands electrons directly to O₂.

## Why does phytanic acid need α-oxidation?

A methyl group on carbon 3 blocks β-oxidation; one carbon is removed first.

## Which peroxisomal transporter fails in X-linked adrenoleukodystrophy?

ABCD1 (ALDP), which imports very-long-chain acyl-CoAs.

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

Sources: [Peroxisomal lipid metabolism](https://reactome.org/PathwayBrowser/#/R-HSA-390918) (Reactome, 2026); [Beta-oxidation of very long chain fatty acids](https://reactome.org/PathwayBrowser/#/R-HSA-390247) (Reactome, 2026); [Alpha-oxidation of phytanate](https://reactome.org/PathwayBrowser/#/R-HSA-389599) (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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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/peroxisomal-oxidation/