What does step 4 of ß-oxidation produce?

In the process of β-oxidation, fatty acids undergo a series of enzymatic reactions to break down into acetyl-CoA units. Step 4 of this process specifically involves the conversion of L-β-hydroxy-acyl-CoA into a fatty acyl-CoA that is shorter by two carbons. This step is crucial for the continuation of β-oxidation, leading to the eventual generation of acetyl-CoA, which can then enter the citric acid cycle for energy production.

During this step, L-β-hydroxy-acyl-CoA is oxidized to form a trans-Δ2-enoyl-CoA intermediate. Following this, a molecule of water is added to the double bond, which is subsequently reduced leading to the formation of a shorter acyl-CoA. This process shortens the fatty acyl chain and prepares it for the next rounds of β-oxidation or for entry into other metabolic pathways.

Thus, the product of step 4 specifically indicates that the primary outcome is the formation of a fatty acyl-CoA that is two carbons shorter than its precursor, making this the correct choice in the context of β-oxidation. This step is fundamental in ensuring that fatty acids are efficiently