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

# Fatty acid synthase (FAS)

Fatty acid synthase is one giant protein with seven activities that builds palmitate two carbons at a time.

Updated 2026-11-01

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## Key facts

- Multifunctional homodimer: KS, MAT, DH, ER, KR, ACP and thioesterase in a single chain.
- Each turn uses one malonyl-CoA and 2 NADPH; after seven turns it releases palmitate (16 C).
- The ACP carries the chain on a phosphopantetheine arm (vitamin B5) from one active site to the next.
- Main product: palmitate; elongation and double bonds are made by other enzymes.

**Also called**
FASN

**EC number**
[2.3.1.85](https://www.enzyme-database.org/query.php?ec=2.3.1.85)

**Genes**
FASN

**Structure (PDB)**
[2PX6](https://www.rcsb.org/structure/2PX6)

## Regulation

- Insulin and a high-carbohydrate diet raise its transcription (SREBP-1c, ChREBP).
- Fasting, glucagon and polyunsaturated fatty acids lower it.

## Inhibitors and toxins

- Cerulenin (blocks KS)
- Orlistat (blocks the thioesterase in vitro)
- Investigational anticancer inhibitors

## Clinical notes

- It is overexpressed in breast, prostate and other cancers; inhibiting it is being studied as treatment.
- In carbohydrate-driven fatty liver, de novo lipogenesis increases.

## Pathways

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

## Related conditions

- [Obesity](https://durgical.com/en/conditions/obesity/)

## Related

- [Malonyl-CoA](https://durgical.com/en/biochemistry/molecules/malonyl-coa/)
- [Palmitate (palmitic acid)](https://durgical.com/en/biochemistry/molecules/palmitate/)
- [Acetyl-CoA](https://durgical.com/en/biochemistry/molecules/acetyl-coa/)
- [Acetyl-CoA carboxylase (ACC)](https://durgical.com/en/biochemistry/enzymes/acetyl-coa-carboxylase/)

## Test yourself

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

## What is the end product of fatty acid synthase?

Palmitate, a saturated 16-carbon fatty acid.

## Which vitamin forms the arm of the acyl carrier protein (ACP)?

Pantothenic acid (B5), as 4'-phosphopantetheine.

## How many enzyme activities does human fatty acid synthase have?

Seven: KS, MAT, DH, ER, KR, ACP and thioesterase, on one chain that forms a dimer.

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

Sources: [FASN: Fatty acid synthase (human)](https://www.uniprot.org/uniprotkb/P49327/entry) (UniProt, 2026); [Fatty acyl-CoA biosynthesis](https://reactome.org/PathwayBrowser/#/R-HSA-75105) (Reactome, 2026); [2PX6: Crystal structure of the thioesterase domain of human fatty acid synthase inhibited by Orlistat](https://www.rcsb.org/structure/2PX6) (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.

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