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

# Cholesterol 7α-hydroxylase (CYP7A1)

Liver CYP7A1 takes the first step in turning cholesterol into bile acids and sets the pace of that pathway.

Updated 2026-11-01

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## Key facts

- Cholesterol + O₂ + NADPH → 7α-hydroxycholesterol: the rate-limiting step of the classic bile acid pathway.
- An endoplasmic reticulum cytochrome P450 found only in hepatocytes.
- Bile acids returning through the enterohepatic circulation repress it (FXR, SHP and ileal FGF19).
- Turning cholesterol into bile acids is the body's main route for getting rid of cholesterol.

**Also called**
CYP7A1

**EC number**
[1.14.14.23](https://www.enzyme-database.org/query.php?ec=1.14.14.23)

**Genes**
CYP7A1

**Structure (PDB)**
[3SN5](https://www.rcsb.org/structure/3SN5)

## Structure

- A 504-residue P450 haemoprotein anchored to the ER membrane.
- Structure 3SN5 shows the human enzyme with the steroid cholest-4-en-3-one in its pocket next to the haem.

## Regulation

- Bile-acid-activated FXR induces SHP in the liver and FGF19 in the ileum: both shut CYP7A1 off.
- It rises when the enterohepatic circulation is interrupted (bile acid sequestrants).
- It follows a circadian rhythm.

## Inhibitors and toxins

- Bile acids (physiological feedback)

## Clinical notes

- Bile acid sequestrants cut the feedback: the liver uses more cholesterol and raises its LDL receptors.
- Variants that reduce CYP7A1 are linked to high LDL and gallstones.
- When bile holds more cholesterol than bile salts and phospholipids can carry, cholesterol stones form.

## Pathways

- [Classic bile acid synthesis pathway](https://durgical.com/en/biochemistry/pathways/classic-bile-acid-synthesis-pathway/)

## Related conditions

- [Gallstones (cholelithiasis)](https://durgical.com/en/conditions/gallstones/)
- [Atherosclerosis and dyslipidaemia](https://durgical.com/en/conditions/atherosclerosis-and-dyslipidaemia/)

## Related

- [Cholic acid](https://durgical.com/en/biochemistry/molecules/cholic-acid/)
- [Cholesterol](https://durgical.com/en/biochemistry/molecules/cholesterol/)
- [Bile acid synthesis](https://durgical.com/en/biochemistry/topics/bile-acid-synthesis/)

## Test yourself

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

## What is the rate-limiting step of bile acid synthesis?

Cholesterol 7α-hydroxylase (CYP7A1), which makes 7α-hydroxycholesterol.

## How do bile acids slow CYP7A1?

They activate FXR, which induces SHP in the liver and FGF19 in the ileum; both repress its gene.

## Why does a bile acid sequestrant lower LDL?

With bile acids lost, CYP7A1 is switched on, the liver uses cholesterol and raises its LDL receptors.

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

Sources: [CYP7A1: Cytochrome P450 7A1 (human)](https://rest.uniprot.org/uniprotkb/P22680.txt) (UniProt, 2026); [3SN5: Crystal structure of human CYP7A1 in complex with cholest-4-en-3-one](https://www.rcsb.org/structure/3SN5) (RCSB Protein Data Bank, 2026); [Synthesis of bile acids and bile salts (R-HSA-192105)](https://reactome.org/PathwayBrowser/#/R-HSA-192105) (Reactome, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/biochemistry/enzymes/cholesterol-7-hydroxylase/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/enzymes/cholesterol-7-hydroxylase/