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
Loading the 3D model…
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.
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
Related conditions
Related
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.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: FASN: Fatty acid synthase (human) (UniProt, 2026); Fatty acyl-CoA biosynthesis (Reactome, 2026); 2PX6: Crystal structure of the thioesterase domain of human fatty acid synthase inhibited by Orlistat (RCSB Protein Data Bank, 2026).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.