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Chapter 23: Q10P (page 1076)

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

Expert verified

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

01

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.

02

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.

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Most popular questions from this chapter

Question:When UMP is dissolved in T2O, exchange of T for H occurs at the 5-position. Propose a mechanism for this exchange.

\(\alpha \)-Keto acids other than \(\alpha \) -ketoglutarate can accept the amino group from pyridoxamine in enzyme catalyzed transamination reactions. What amino acids are formed when the following a-keto acids accept the amino group?

Nonenzyme-bound FAD is a stronger oxidizing agent than NAD+. How, then, can NAD+oxidize the reduced flavoenzyme in the pyruvate dehydrogenase

complex?

Explain why the ability of PLP to catalyze an amino acid transformation is greatly reduced if the OH substituent of pyridoxal phosphate is replaced by OCH3.

The enzyme that catalyzes the Cα-Cβbond cleavage reaction that converts serine to glycine removes the substituent (R) bonded to the \(\alpha \)-carbon in the first step of the reaction. Starting with PLP bound to serine in an imine linkage, propose a mechanism for this reaction. (Hint:The first step involves removal of the proton from serine’s OH group.)
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