The image below shows the reactions of the Beta-oxidation pathway. Label the enzymes on the diagram. (Note that enoyl-CoA hydratase is sometimes called enoyl-CoA hydrase, and acyl-CoA acetyltransferase is also called thiolase.)
The Correct Answer and Explanation is :
The β-oxidation pathway is a metabolic process that breaks down fatty acids into acetyl-CoA units, which then enter the citric acid cycle to produce energy. This pathway involves a recurring cycle of four enzymatic reactions, each catalyzed by a specific enzyme:
- Acyl-CoA Dehydrogenase: This enzyme initiates the β-oxidation cycle by catalyzing the dehydrogenation of acyl-CoA, introducing a trans double bond between the α (C2) and β (C3) carbon atoms, resulting in the formation of trans-Δ²-enoyl-CoA. This reaction involves the reduction of FAD to FADH₂. (en.wikipedia.org)
- Enoyl-CoA Hydratase: Also known as enoyl-CoA hydrase, this enzyme hydrates the double bond in trans-Δ²-enoyl-CoA, adding a water molecule to form L-3-hydroxyacyl-CoA. This step is stereospecific, ensuring the correct configuration for subsequent reactions. (en.wikipedia.org)
- 3-Hydroxyacyl-CoA Dehydrogenase: This enzyme oxidizes L-3-hydroxyacyl-CoA by converting the hydroxyl group on the β-carbon into a keto group, forming 3-ketoacyl-CoA. NAD⁺ serves as the electron acceptor in this reaction, being reduced to NADH. (en.wikipedia.org)
- Acyl-CoA Acetyltransferase (Thiolase): Commonly referred to as thiolase, this enzyme cleaves 3-ketoacyl-CoA by introducing a CoA molecule, resulting in the release of one acetyl-CoA unit and an acyl-CoA shortened by two carbon atoms. The shortened acyl-CoA re-enters the β-oxidation cycle for further processing. (en.wikipedia.org)
Each cycle of β-oxidation shortens the fatty acid chain by two carbon units, producing one molecule each of acetyl-CoA, FADH₂, and NADH. The acetyl-CoA enters the citric acid cycle, while FADH₂ and NADH donate electrons to the electron transport chain, ultimately contributing to ATP synthesis. This systematic breakdown of fatty acids is essential for energy production, especially during periods of fasting or increased energy demand.
Understanding the specific roles of these enzymes is crucial, as deficiencies or malfunctions can lead to metabolic disorders. For instance, a deficiency in acyl-CoA dehydrogenase can impair the initial step of β-oxidation, leading to the accumulation of unmetabolized fatty acids and associated health issues. (ncbi.nlm.nih.gov)
In summary, the β-oxidation pathway is a vital metabolic process involving a series of enzymatic reactions that efficiently convert fatty acids into energy, highlighting the importance of each enzyme’s role in maintaining metabolic health.