Biochemistry · Enzyme
Squalene epoxidase !
Squalene epoxidase activates squalene with oxygen so it can close into rings; it is the second control point of cholesterol synthesis.
Updated 2026-11-01
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Key facts
- Squalene + O₂ + NADPH → 2,3-oxidosqualene + H₂O; it uses FAD and gets electrons from cytochrome P450 reductase.
- It sits in the endoplasmic reticulum membrane.
- It is the second control point after HMG-CoA reductase: cholesterol speeds its degradation.
- Terbinafine inhibits the enzyme of fungi, which make ergosterol, and barely affects the human one.
- Also called
- Squalene monooxygenase (SQLE)
- EC number
- 1.14.14.17
- Genes
- SQLE
- Structure (PDB)
- 6C6P
Structure
- A 574-residue flavoprotein with an FAD-binding and a substrate-binding domain, attached to the membrane.
- Structure 6C6P shows the human catalytic domain with FAD and the inhibitor NB-598 in the substrate pocket.
Regulation
- Cholesterol promotes its ubiquitination by MARCHF6 and its degradation.
- SREBP-2 raises its transcription.
Inhibitors and toxins
- Allylamines: terbinafine, naftifine (antifungals)
- NB-598 (experimental)
Clinical notes
- Terbinafine treats onychomycosis and tinea: the fungus builds up toxic squalene and runs out of ergosterol.
- SQLE is increased in some tumours and is studied as a cancer target.
Pathways
Related
Test yourself
Think of the answer, then tap the question to see it.
What reaction does squalene epoxidase catalyse?
It turns squalene into 2,3-oxidosqualene using O₂, NADPH and FAD.
Why does terbinafine kill the fungus without much harm to the person?
It is far more potent on the fungal squalene epoxidase; the fungus accumulates squalene and lacks ergosterol.
What makes it a second control point of the pathway?
Cholesterol speeds its degradation and SREBP-2 controls its transcription.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: SQLE: Squalene monooxygenase (human) (UniProt, 2026); 6C6P: Human squalene epoxidase (SQLE, squalene monooxygenase) structure with FAD and NB-598 (RCSB Protein Data Bank, 2026); Cholesterol biosynthesis (R-HSA-191273) (Reactome, 2026).
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Representative model, for educational purposes only.