Fatty acids are activated for beta-oxidation through a two-step process that primarily occurs in the cytosol and mitochondria. Here's a breakdown:
Activation in the Cytosol
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Conjugation with Coenzyme A (CoA): In the cytosol, fatty acids are activated by attaching to coenzyme A (CoA). This reaction is catalyzed by fatty acyl-CoA synthetase, forming a fatty acyl-CoA molecule. This is the key activation step that "primes" the fatty acid for further processing in beta-oxidation.
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The Result: The resulting fatty acyl-CoA molecule is now ready for transport into the mitochondria, where beta-oxidation takes place.
Transport into the Mitochondria
- Carnitine Palmitoyltransferase 1 (CPT1): Because fatty acyl-CoA molecules can't directly cross the inner mitochondrial membrane, they must undergo modification. The enzyme CPT1, located on the outer mitochondrial membrane, transfers the fatty acyl group from CoA to carnitine, forming acylcarnitine.
- Carnitine Translocase (CAT): The acylcarnitine molecule can then be transported across the inner mitochondrial membrane via the carnitine translocase (CAT). Once inside the mitochondrial matrix, the fatty acid is then detached from carnitine by a different enzyme (CPT2). This regenerates the fatty acyl-CoA, which is now accessible to the enzymes of beta-oxidation.
Summary Table
| Step | Location | Enzyme(s) Involved | Function |
|---|---|---|---|
| Fatty Acid Activation | Cytosol | Fatty acyl-CoA synthetase | Attaches fatty acid to CoA, forming fatty acyl-CoA |
| Transport to Mitochondria | Outer mitochondrial membrane, inner mitochondrial membrane | CPT1, carnitine translocase (CAT), CPT2 | Transfers fatty acyl group to carnitine, transports to matrix, reconstitutes fatty acyl-CoA for oxidation |
This entire process ensures that fatty acids are properly prepared and transported to the site of beta-oxidation, where they can be broken down to produce energy. The reference provided confirms that:
Fatty acids are activated for degradation by conjugation with coenzyme A (CoA) in the cytosol. The long-chain fatty-acyl-CoA is then modified by carnitine palmitoyltransferase 1 (CPT1) to acylcarnitine and transported across the inner mitochondrial membrane by carnitine translocase (CAT).18-May-2021
