Question

Acetolactatesynthasetransfers the acyl group of pyruvate to \(\alpha \)-ketobutyrate. This is the first step in the biosynthesis of the amino acid isoleucine. Propose a mechanism for this reaction.

Short answer

In question it is mentioned that acetolactate synthase enzyme needs TTP for transferring acyl group from pyruvate to alpha-ketobutyrate to form alpha-aceto-alpha-hydroxybutyrate and remove carbon-dioxide.

Step-by-step solution

Acetolactate synthase role

In question it is mentioned that acetolactate synthase enzyme needs TTP for transferring acyl group from pyruvate to alpha-ketobutyrate to form alpha-aceto-alpha-hydroxybutyrate and remove carbon-dioxide.

Mechanism of action

The mechanism for the reaction is as follows:

• First step is proton removal from TPP forming TPP-ylide.
• TPP-ylide attaches to the carbonyl carbon of pyruvate.
• The tetrahedral intermediate formed here easily undergoes decarboxylation by reaction giving TPP-enamine.
• Addition of alpha-ketobutyrate occurs on the TPP-enamine carbon and afterward elimination from the tetrahedral intermediate occur forming alpha-aceto-alpha-hydroxybutyrate and regenerates the TPP-ylide.