Formation and Stability of a Vinyl Carbanion at the Active Site of Orotidine 5‘-Monophosphate Decarboxylase: p K a of the C-6 Proton of Enzyme-Bound UMP
Citations Over TimeTop 10% of 2008 papers
Abstract
We report that orotidine 5‘-monophosphate decarboxylase (OMPDC) catalyzes exchange of the C-6 proton of uridine 5‘-monophosphate (UMP) for deuterium from solvent in D2O at 25 °C and pD 7.0−9.3. Kinetic analysis of deuterium exchange gives pKa ≤ 22 for carbon deprotonation of enzyme-bound UMP, which is at least 10 units lower than that for deprotonation of an analogue of UMP in water. The observation of enzyme-catalyzed deuterium exchange via a stabilized carbanion provides convincing evidence for the decarboxylation of orotidine 5‘-monophosphate (OMP) by OMPDC to give the same carbanion intermediate. The data show that yeast OMPDC stabilizes the bound vinyl carbanion by at least 14 kcal/mol. We conclude that OMPDC also provides substantial stabilization of the late carbanion-like transition state for the decarboxylation of OMP, and that this transition state stabilization constitutes a large fraction, but probably not all, of the enormous 1017-fold enzymatic rate acceleration.
Related Papers
- → Heterolytic Activation of H−X (X = H, Si, B, and C) Bonds: An Experimental and Theoretical Investigation(2007)53 cited
- → Homolytic vs Heterolytic Paths in the Photochemistry of Haloanilines(2003)72 cited
- → Reactions of transition metal carbonyl anions with 2-(1-bromoalkylidene)thiazolidin-4-ones: halogenophilic attack or deprotonation(2010)5 cited
- → Heterolytic σ ‐Bond Activation by Transition Metal Complexes(2008)1 cited
- → Mechanistic pathways in phosphate ester photochemistry(1991)1 cited