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.

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.

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.

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.

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

Sources: Peroxisomal lipid metabolism (Reactome, 2026); Beta-oxidation of very long chain fatty acids (Reactome, 2026); Alpha-oxidation of phytanate (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.