Omega oxidation (ω-oxidation) of fatty acid


Omega oxidation (ω-oxidation) is a process of fatty acid metabolism that occurs in some animals and plants. It involves the introduction of a hydroxyl group at the terminal carbon atom (omega carbon) of a fatty acid chain, followed by oxidation to form a dicarboxylic acid.

In vertebrates, the enzymes for ω-oxidation are located in the smooth endoplasmic reticulum (ER) of liver and kidney cells. The smooth ER is a membrane-bound organelle that contains various enzymes involved in lipid synthesis and detoxification. The location of ω-oxidation in the smooth ER distinguishes it from β-oxidation, which occurs in the mitochondria.

The smooth ER is also the site of cytochrome P450 enzymes, which are involved in the first step of ω-oxidation. Cytochrome P450 enzymes are a family of heme-containing proteins that catalyze the insertion of oxygen into organic molecules. They use molecular oxygen (O2) and NADPH as substrates and produce water (H2O) as a byproduct. Cytochrome P450 enzymes are responsible for the hydroxylation of the omega carbon of fatty acids, as well as many other reactions involved in drug metabolism and biosynthesis of hormones and cholesterol.

The location of ω-oxidation in the smooth ER allows it to act on medium to long chain fatty acids (10-12 carbon atoms), which are more abundant in the cytosol than in the mitochondria. The products of ω-oxidation can then enter the mitochondria and undergo β-oxidation by the normal route, or be used for other metabolic pathways. For example, some dicarboxylic acids can enter the citric acid cycle as succinyl-CoA, or be used for gluconeogenesis under conditions of starvation and diabetes.

Omega oxidation is a subsidiary pathway for fatty acid degradation that can compensate for impaired β-oxidation. It also plays important roles in the production of insect pheromones, plant biopolyesters, and signaling molecules.