Determination of the Mechanism of Orotidine 5‘-Monophosphate Decarboxylase by Isotope Effects

1 April 2000

journal article
Published by American Chemical Society (ACS) in Biochemistry

Vol. 39 (16) , 4569-4574
https://doi.org/10.1021/bi000376p

Abstract

Orotidine 5‘-monophosphate shows a ¹⁵N isotope effect of 1.0036 at N-1 for decarboxylation catalyzed by orotidine 5‘-monophosphate decarboxylase. Picolinic acid shows a ¹⁵N isotope effect of 0.9955 for decarboxylation in ethylene glycol at 190 °C, while N-methyl picolinic acid shows a ¹⁵N isotope effect of 1.0053 at 120 °C. The transition state for enzymatic decarboxylation of orotidine 5‘-monophosphate resembles the transition state for N-methyl picolinic acid in that no bond order changes take place at N-1. This rules out enolization to give a quaternary nitrogen at N-1 in the enzymatic mechanism and suggests a carbanion intermediate stabilized by simple electrostatic interaction with Lys-93. The driving force for the reaction appears to be ground-state destabilization resulting from charge repulsion between the carboxyl of the substrate and Asp-91.

Keywords

This publication has 1 reference indexed in Scilit:

The Mechanism of Orotidine 5‘-Monophosphate Decarboxylase: Catalysis by Destabilization of the Substrate
Biochemistry, 2000