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Chapter 24: Problem 15

Write a suitable reaction mechanism for the \(\beta\) -ketoacyl-ACP synthase, showing how the involvement of malonyl-CoA drives this reaction forward.

Short Answer

Expert verified
The enzyme forms an acyl-enzyme intermediate while malonyl-CoA undergoes decarboxylation. Then, the enolate attacks the carbonyl group of the intermediate, forming a \(\beta\)-ketoacyl-ACP and releasing a lot of energy that drives the reaction forward. The product is eventually released and the enzyme goes back to its original state.

Step by step solution

01

Identification of Reagents

First, identify the reagents in this reaction. We have the enzyme \(\beta\)-ketoacyl-ACP synthase and malonyl-CoA. The enzyme has an active site where the reaction will occur and malonyl-CoA is a substrate that will be processed by the enzyme.
02

Formation of Acyl-enzyme Intermediate

In this step, the enzyme initiates the reaction by forming an acyl-enzyme intermediate. The active site cysteine of the enzyme attacks the carbonyl carbon of the acyl-CoA, forming a covalent bond and releasing CoA. This results in a thioester intermediate.
03

Decarboxylation of Malonyl-CoA

Next, the malonyl-CoA undergoes decarboxylation, where it loses a molecule of carbon dioxide. This is an important step that releases a lot of energy, which pushes the reaction forward.
04

Formation of Stable Product

The nucleophilic enolate produced from the previous step attacks the carbonyl group of the acyl-enzyme intermediate. This way, a \(\beta\)-ketoacyl-ACP is formed along with carbon dioxide. The high-energy bond between the enzyme and the \(\beta\)-ketoacyl group is hydrolyzed to release the product.
05

Completing the Reaction

Now that the \(\beta\)-ketoacyl-ACP is released, the enzyme returns to its initial state, ready to process another molecule of malonyl-CoA.

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