Omega oxidation (ω-oxidation) of fatty acid

  • Omega oxidation (ω-oxidation) is a process of fatty acid metabolism in some species of animals.
  • It is an alternative pathway to beta oxidation that, instead of involving the β carbon, involves the oxidation of the ω carbon (the carbon most distant from the carboxyl group of the fatty acid).
  • The ω (omega)-carbon (the methyl carbon) of fatty acids is oxidized to a carboxyl group in the endoplasmic reticulum.
  • The process is normally a minor catabolic pathway for medium-chain fatty acids (10-12 carbon atoms), but becomes more important when β oxidation is defective (because of mutation or a carnitine deficiency, for example).

Omega oxidation (ω-oxidation) of fatty acid

Location of Omega oxidation

In vertebrates, the enzymes for ω oxidation are located in the smooth ER of liver and kidney cells, instead of in the mitochondria as with β-oxidation.

  • Substrate: Medium to Long chain fatty acids (Fatty acid with 10-12 carbon atoms).
  • End Product: Dicarboxylic acids are produced.

Steps in ω-oxidation of Fatty acids

  • The first step introduces a hydroxyl group onto the ω-carbon.
    • The oxygen for this group comes from molecular oxygen (O2) in a complex reaction that involves cytochrome P450 and the electron donor NADPH.
    • Reactions of this type are catalyzed by mixed function oxidases.
  • Two more enzymes now act on the ω carbon:
    • Alcohol dehydrogenase oxidizes the hydroxyl group to an aldehyde, and
    • Aldehyde dehydrogenase oxidizes the aldehyde group to a carboxylic acid, producing a fatty acid with a carboxyl group at each end.
  • At this point, either end can be attached to coenzyme A, or the molecule can enter the mitochondrion and undergo β-oxidation by the normal route.
  • In each pass through the oxidation pathway, the “double-ended” fatty acid yields dicarboxylic acids such as succinic acid, which can enter the citric acid cycle, and adipic acid.

Significance of Omega oxidation

  • It is a subsidiary pathway for β-oxidation of fatty acids when β-oxidation is blocked.
  • It is observed that ω- and (ω-1)-oxidation of fatty acids are related to energy metabolism in some laboratory animals such as musk shrews and Mongolian gerbils.
  • Studies confirm that ω- and (ω-1)-oxidation of fatty acids play crucial roles in the production of insect pheromones of honeybees and in the formation of biopolyesters of higher plants.
  • Many studies also have demonstrated that the ω-oxidation serves to provide succinyl-CoA for the citric acid cycle and for gluconeogenesis under conditions of starvation and diabetes.

References

  1. Smith, C. M., Marks, A. D., Lieberman, M. A., Marks, D. B., & Marks, D. B. (2005). Marks’ basic medical biochemistry: A clinical approach. Philadelphia: Lippincott Williams & Wilkins.
  2. https://www.slideshare.net/AnupShamsherBudhatho/fatty-acid-oxidation-beta-alpha-omega-and-peroxisomal
  3. MIURA Y. The biological significance of ω-oxidation of fatty acids. Yamakawa T, ed. Proceedings of the Japan Academy Series B, Physical and Biological Sciences. 2013;89(8):370-382. doi:10.2183/pjab.89.370.
  4. https://en.wikipedia.org/wiki/Omega_oxidation

About Author

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Sagar Aryal

Sagar Aryal is a microbiologist and a scientific blogger. He attended St. Xavier’s College, Maitighar, Kathmandu, Nepal, to complete his Master of Science in Microbiology. He worked as a Lecturer at St. Xavier’s College, Maitighar, Kathmandu, Nepal, from Feb 2015 to June 2019. After teaching microbiology for more than four years, he joined the Central Department of Microbiology, Tribhuvan University, to pursue his Ph.D. in collaboration with Helmholtz-Institute for Pharmaceutical Research Saarland (HIPS), Saarbrucken, Germany. He is interested in research on actinobacteria, myxobacteria, and natural products. He has published more than 15 research articles and book chapters in international journals and well-renowned publishers.

2 thoughts on “Omega oxidation (ω-oxidation) of fatty acid”

  1. I would like to thank you for the condensed notes, it is more than a helpful to do a comparison between the three types of oxidation.

    Reply

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