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The Mechanism of Orotidine 5‘-Monophosphate Decarboxylase: Catalysis by Destabilization of the Substrate

2000; American Chemical Society; Volume: 39; Issue: 7 Linguagem: Inglês

10.1021/bi992553w

1943-295X

Wan Yong Feng, Travis J. Austin, Frank Chew, Scott Gronert, Weiming Wu,

Photosynthetic Processes and Mechanisms

The mechanism of orotidine 5'-monophosphate decarboxylase (OMP decarboxylase, ODCase) was studied using the decarboxylation of orotic acid analogues as a model system. The rate of decarboxylation of 1,3-dimethylorotic acid and its analogues as well as the stability of their corresponding carbanion intermediates was determined. The results have shown that the stability of the carbanion intermediate is not a critical factor in the rate of decarboxylation. On the other hand, the reaction rate is largely dependent on the equilibrium constant for the formation of a zwitterion. Based on these results, we have proposed a new mechanism in which ODCase catalyzes the decarboxylation of OMP by binding the substrate in a zwitterionic form and providing a destabilizing environment for the carboxylate group of OMP.