[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › Cytochrome P450 2E1 (CYP2E1, MEOS)

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

# Cytochrome P450 2E1 (CYP2E1, MEOS)

A liver enzyme that oxidises ethanol in heavy drinkers and turns acetaminophen and other toxins into harmful products.

Updated 2026-11-01

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## Key facts

- A haem monooxygenase in the hepatocyte endoplasmic reticulum (most abundant in centrilobular zone 3).
- Ethanol + NADPH + O₂ → acetaldehyde + NADP⁺ + 2 H₂O; it has a high Km, so it works when alcohol is plentiful.
- Chronic drinking induces it (mainly by stabilising the protein): more tolerance and more free radicals.
- It activates toxins: acetaminophen → NAPQI, carbon tetrachloride, benzene, nitrosamines; this is why chronic drinkers are more sensitive to them.

**Also called**
Microsomal ethanol-oxidising system (MEOS)

**EC number**
[1.14.14.1](https://www.enzyme-database.org/query.php?ec=1.14.14.1)

**Genes**
CYP2E1

**Structure (PDB)**
[3E4E](https://www.rcsb.org/structure/3E4E)

## Structure

- Membrane protein with the typical P450 fold; its active pocket is small, suited to little molecules such as ethanol, acetone or pyrazoles.

## Regulation

- Induced by ethanol, acetone, isoniazid and prolonged fasting or uncontrolled diabetes (ketone bodies).
- Ethanol that is present competes with other substrates: acute drinking inhibits it and chronic drinking induces it.

## Inhibitors and toxins

- Disulfiram (through its metabolite diethyldithiocarbamate)
- 4-Methylpyrazole (fomepizole, the one in the 3D structure)
- Clomethiazole

## Clinical notes

- Chronic drinkers suffer acetaminophen liver injury with smaller amounts: more CYP2E1 makes more NAPQI, and they have less glutathione.
- Its «leaky» cycle releases superoxide and hydrogen peroxide: lipid peroxidation in alcoholic liver disease.
- It explains part of the metabolic tolerance to alcohol in habitual drinkers.

## Pathways

- [Ethanol metabolism](https://durgical.com/en/biochemistry/pathways/ethanol-metabolism/)

## Related conditions

- [Acetaminophen toxicity](https://durgical.com/en/conditions/acetaminophen-toxicity/)
- [Alcoholic liver disease (biochemistry)](https://durgical.com/en/conditions/alcoholic-liver-disease/)

## Related

- [Cytochrome P450 system](https://durgical.com/en/biochemistry/topics/cytochrome-p450-system/)
- [Alcohol dehydrogenase (ADH)](https://durgical.com/en/biochemistry/enzymes/alcohol-dehydrogenase/)
- [NAPQI (N-acetyl-p-benzoquinone imine)](https://durgical.com/en/biochemistry/molecules/napqi/)
- [Acetaminophen metabolism and NAPQI](https://durgical.com/en/biochemistry/topics/acetaminophen-metabolism-and-napqi/)
- [Ethanol](https://durgical.com/en/biochemistry/molecules/ethanol/)
- [Heme](https://durgical.com/en/biochemistry/molecules/heme/)
- [NADPH](https://durgical.com/en/biochemistry/molecules/nadph/)
- [Reactive oxygen species and antioxidants](https://durgical.com/en/biochemistry/topics/reactive-oxygen-species-and-antioxidants/)
- [Fomepizole (4-methylpyrazole)](https://durgical.com/en/biochemistry/molecules/fomepizole/)

## Test yourself

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

## Why is a chronic drinker more vulnerable to acetaminophen?

They have more CYP2E1, which makes more NAPQI, and less glutathione to neutralise it.

## Which reduced coenzyme does CYP2E1 use to oxidise ethanol?

NADPH (with O₂), unlike alcohol dehydrogenase, which uses NAD⁺.

## In which zone of the liver lobule is CYP2E1 abundant and what follows?

In zone 3 (centrilobular); that is where acetaminophen necrosis begins.

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

Sources: [CYP2E1: Cytochrome P450 2E1 (human), UniProt P05181](https://www.uniprot.org/uniprotkb/P05181/entry) (UniProt, 2026); [RCSB PDB - 3E4E: Human cytochrome P450 2E1 in complex with the inhibitor 4-methylpyrazole](https://www.rcsb.org/structure/3E4E) (RCSB Protein Data Bank, 2026); [Cytochrome P450 - arranged by substrate type](https://reactome.org/PathwayBrowser/#/R-HSA-211897) (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/enzymes/cytochrome-p450-2e1/