Friday, May 7, 2021
Mitochondrial Health

Carnitine Carrier System | Beta Oxidation Part II

The mitochondrial membrane is not permeable to long-chain fatty acids; a multi-step process is therefore required for these compounds to be used by mitochondria. In the muscle cytoplasm, long-chain fatty acids are first activated by long-chain acyl-CoA synthetase (ACS) to their CoA thioesters. The CoA thioesters are subsequently linked with carnitine by the enzyme carnitine palmitoyltransferase I (CPT I) located on the inner side of the outer mitochondrial membrane. The acylcarnitine form of the long-chain fatty acid, palmitoylcarnitine, is then transferred across the inner mitochondrial membrane by carnitine:acylcarnitine translocase. Once in the mitochondrial matrix, it is converted back to free acyl-CoA derivative and carnitine by carnitine palmitoyltransferase II (CPT II) on the inner side of the inner mitochondrial membrane. Once carnitine is released, the long-chain acyl-CoA derivative enters the beta-oxidation pathway. With every complete cycle, a two-carbon fragment is cleaved and an acetyl-CoA molecule is released.


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27 thoughts on “Carnitine Carrier System | Beta Oxidation Part II
  1. Nice. Here, some more details/notes from that I took for those interested:

    The enzymes that oxidize fatty acids in animal cells are located in the mitochondrial matrix. Large FFAs cannot pass through the mitochondria membrane directly, so they need to be transported which is achieved via three enzymatic reactions of the carnitine shuttle.
    The first of these reactions is catalyzed by Acyl-CoA synthetase which promote the general reaction: Fatty acid + CoA + ATP —> fatty acyl-CoA + AMP + PPi.
    These fatty acyl-CoAs can then be transported to matrix of mitochondria where they can undergo oxidation to produce ATP or they can remain in cytosol to produce membrane lipids. To transport these fatty acyl-CoAs to the matrix, they attach to the hydroxyl group of carnitine to form the fatty acyl-carnitine—the second reaction of the carnitine shuttle. The fatty acyl-carnitines then enters the matrix via facilitated diffusion through the acyl-carnitine/carnitine transporter. Once inside the matrix, the fatty acyl group is enzymatically transferred from carnitine to the intramitochondrial coenzyme A by carnitine acyl transferase II, regenerating fatty acyl-CoA and releasing it. The carnitine-mediated entry process is the rate-limiting step for oxidation of fatty acids in mitochondria. The rate of transfer of long-chain fatty acyl-CoA in mitochondria is the limiting step of β-oxidation.

    Let me know if I made any mistake

  2. You forgot to mention the carnitine acylcarnitine translocase and the conjugate it forms with the fatty acyl to transport it across the mitchondrial intermembrane space. Although some sources have said that they're not sure whether or not carnitine acylcarnitine translocase is located in the outer mitochondrial membrane or intermembrane space.

  3. Sir plz make vidio on1) types of plant pathogen, 2)mode of entry of plant pathogen into plant host & plant disease resistance 3) general symptoms, transmission & control of plant disease

  4. Sir please explain why 2 ATPs are required for the activation of Palmitic acid.. because in textbook pathways and even in your diagram.. only 1 ATP is shown for a fatty acid.. is there some kind of cleavage beforehand itself????

  5. You didn't explain the first step.
    In first step, acyl-CoA synthetase catalyze the formation of fatty acid and coenzyme A to yield Fatty acyl-CoA with help of ATP which is converted into AMP and 2PPi (occurs in cytosol).

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