Beta-oxidation is the major degradative pathway for fatty acid esters in humans. Fatty acids and their CoA esters are found throughout the body, playing roles such as components of cellular lipids, regulators of enzymes and membrane channels, ligands for nuclear receptors, precursor molecules for hormones, and signalling molecules. Beta-oxidation occurs in the peroxisomes and mitochondria, the latter of which is depicted here. Whether beta-oxidation starts in the mitochondria or the peroxisome depends on the length of the fatty acid. Medium to long chain fatty acids go directly to the mitochondria, whereas very long chain fatty acids (>22 carbons) may be first metabolized down to octanyl-CoA in the peroxisomes and then transported to the mitochondria for the remainder of the oxidation. Beta-oxidation begins with fatty acids first being activated by an acyl-coenzyme A synthetase. This process uses ATP to produce a reactive fatty acyl adenylate which then reacts with coenzyme A to produce a fatty acyl-CoA. Short and medium chain fatty acids can enter the mitochondria directly via diffusion where they are activated in the mitochondrial matrix by acyl-coenzyme A synthetases. Long chain fatty acids must be activated in the outer mitochondrial membrane then transported as a carnatine complex into the mitochondria. A double bond is formed between C-2 and C-3 to produce trans-Δ2-enoyl-CoA which is catalyzed by acyl-CoA-dehydrogenases in the mitochondria. Enoyl CoA hydratase then hydrates the double bond between C-2 and C-3 to produce a L-beta-hydroxyacyl CoA which then has its hydroxyl group converted to a keto group to produce beta-ketoacyl CoA. Finally, the beta-ketoacyl CoA is cleaved by beta-ketothiolase and a thiol group is inserted between C-2 and C-3 to reduce the acyl-CoA and produce acetyl-CoA. Acetyl-CoA can then enter the citric acid cycle.

Mitochondrial Beta-Oxidation of Short Chain Saturated Fatty Acids References