Chorismate Mutase - Mechanism of Catalysis

Mechanism of Catalysis

The mechanism for the transformation of chorismate to prephenate is formally a Claisen rearrangement. This transformation is the first committed step in the pathway to production of the aromatic amino acids: tyrosine and phenylalanine. In the absence of enzyme catalysis this mechanism proceeds as a concerted, but asynchronous step and is an exergonic process. As a result there is no formal intermediate, but rather a chair-like transition state. The addition of chorismate mutase, increases the rate of the reaction a million fold. There have been extensive studies on the exact mechanism of this reaction, but the rate-determining step has yet to be uncovered. Some questions that remain surrounding the mechanism are how conformational constraint of the flexible substrate, specific hydrogen bonding to the transition state, and electrostatic interactions actually contribute to catalysis. One study using CM from B. subtilis showed evidence that the when a cation was aptly placed in the active site, the electrostatic interactions between it and the negatively charged transition state promoted catalysis.