Omega oxidation
Omega 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 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.
In vertebrates, the enzymes for ω oxidation are located in the endoplasmic reticulum of liver and kidney cells, instead of in the mitochondria as with β oxidation. The steps of the process are as follow:
| Hydroxylation | mixed function oxidase | The first step introduces a hydroxyl group onto the ω carbon. The oxygen for the group comes from molecular oxygen in a complex reaction that involves cytochrome P450 and the electron donor NADPH. | 
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| Oxidation | alcohol dehydrogenase | The next step is the oxidation of the hydroxyl group to an aldehyde by NAD+. | 
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| Oxidation | aldehyde dehydrogenase | The third step is the oxidation of the aldehyde group to a carboxylic acid by NAD+. The product of this step is a fatty acid with a carboxyl group at each end. | 
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After the three steps, either end of fatty acid can be attached to coenzyme A. The molecule can enter the mitochondrion and undergo β oxidation. The final products after successive oxidation include succinic acid, which can enter citric acid cycle, and adipic acid.
References
- Nelson, D. L. & Cox, M. M. (2005). Lehninger Principles of Biochemistry, 4th Edition. New York: W. H. Freeman and Company, pp. 648-649. ISBN 0-7167-4339-6.