AAT Bioquest

What are the steps of beta oxidation?

Posted October 12, 2023


Beta oxidation consists of four main steps: 

  1. Dehydrogenation – In this step, acyl CoA is oxidized by the enzyme acyl CoA dehydrogenase, which catalyzes the removal of two hydrogens between carbons 2 and 3 (C2 and C3), forming a double bond between the alpha and beta carbons in the fatty acyl-CoA molecule. The end product of this reaction is trans-delta 2-enoyl CoA. 
  2. Hydration – In this step, the double bond between C2 and C3 of trans-delta 2-enoyl CoA is hydrated in a reaction catalyzed by the enzyme enoyl CoA hydratase. The addition of water (H2O) results in the formation of   L-β-hydroxyacyl CoA, which has a hydroxyl group (-OH) in C2, in place of the double bond. 
  3. Oxidation – The third step involves another dehydration reaction, which is similar to that in the first step but occurs at a different position on the fatty acyl-CoA molecule. During this reaction, 2 hydrogen atoms are removed from the beta carbon, which now contains a hydroxyl group from Step 2. This reaction is catalyzed by the enzyme 3-hydroxyacyl-CoA dehydrogenase, which generates NADH+ H and beta-ketoacyl CoA. 
  4. Thiolysis – In this final step, the enzyme thiolase cleaves the terminal acetyl-CoA group (between the alpha and beta carbons), resulting in the formation of a new acyl-CoA, which is shortened by 2 carbon atoms. The shortened acyl-CoA chain can re-enter the beta-oxidation cycle, repeating the series of reactions until the entire fatty acid has been broken down into acetyl-CoA molecules. Acetyl-CoA molecules enter the citric acid cycle to generate ATP. 
Additional resources

Mitochondrial β-oxidation of saturated fatty acids in humans

Cell Meter™ Intracellular Colorimetric Lipid Peroxidation (MDA) Assay Kit