Fatty acid synthase (FASN) works by catalyzing the synthesis of fatty acids through a series of precisely coordinated enzymatic reactions. The process can be broken down into three major steps, as outlined by the reference material.
The Three Major Steps of Fatty Acid Synthesis by FASN:
The synthesis process involves a repeating cycle to elongate the fatty acid chain. These cycles occur in the following way:
-
Initiation:
- This first step is where the process begins.
- It involves the condensation of malonyl-CoA and acetyl-CoA.
- This reaction is catalyzed by malonyl/acetyl-CoA-transacylase (MAT).
-
Elongation:
- This involves a series of reduction and dehydration reactions.
- Each cycle adds two carbons to the growing fatty acid chain.
- This part is performed by:
- KS (β-ketoacyl synthase)
- DH (β-hydroxyacyl dehydratase)
- ER (enoyl reductase)
- KR (β-ketoacyl reductase)
- The cycle repeats, each time lengthening the fatty acid chain by two carbon atoms.
-
Termination:
- The process terminates when the fatty acid chain reaches the desired length (usually 16 carbons, palmitic acid).
- The completed fatty acid is released from the FASN complex.
Summary in Table Format:
| Step | Description | Enzymes Involved |
|---|---|---|
| Initiation | Condensation of malonyl-CoA and acetyl-CoA | MAT |
| Elongation | Repeated cycle of reduction and dehydration, adding two carbons each cycle | KS, DH, ER, KR |
| Termination | Release of the completed fatty acid chain | - |
How the Cycle Works
The elongation cycle is critical for fatty acid synthesis and is driven by the following reactions:
- Condensation: The KS enzyme catalyzes the reaction of malonyl-CoA with the growing fatty acid chain.
- Reduction: The KR enzyme reduces the keto group to a hydroxyl group.
- Dehydration: The DH enzyme removes a water molecule to create a double bond.
- Reduction: The ER enzyme reduces the double bond to a single bond, completing the addition of the two carbon atoms.
Importance
Fatty acid synthase is essential for producing fatty acids needed for cell membranes, energy storage, and other important biological functions. Understanding its mechanisms can help with exploring treatments for diseases related to fatty acid metabolism.
