Orotidine 5'-monophosphate decarboxylase (OMPDC) employs no metal ions or other cofactors but yet effects an enormous 1017-fold acceleration of the decarboxylation of orotidine 5'-monophosphate (OMP) to give uridine 5'-monophosphate (UMP).  Exogenous phosphite dianion strongly activates OMPDC for catalysis of  the decarboxylation and deuterium exchange reactions, respectively, of truncated analogs of OMP and UMP. This shows that the dianion binding energy is used in the stabilization of the vinyl carbanion that forms in both the decarboxylation and deuterium exchange reactions. The mechanism by which the binding energy of the nonreacting dianion substrate piece is used in the stabilization of a vinyl carbanion that forms at a separate site on the protein is not understood.  The highlights of studies to address this problem will be presented and shown to provide support for a model in which the dianion binding energy is used to stabilize a rare, but catalytically active form of OMPDC.

Binding energy and catalysis by orotidine 5'-phosphate decarboxylase: The mechanism for activation of the enzyme by dianions

242nd National Meeting (2011)

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