Product deuterium isotope effects for orotidine 5'-monophosphate decarboxylase: effect of changing substrate and enzyme structure on the partitioning of the vinyl carbanion reaction intermediate.

ABSTRACT: A product deuterium isotope effect (PIE) of 1.0 was determined as the ratio of the yields of [6-(1)H]-uridine 5'-monophosphate (50%) and [6-(2)H]-uridine 5'-monophosphate (50%) from the decarboxylation of orotidine 5'-monophosphate (OMP) in 50/50 (v/v) HOH/DOD catalyzed by orotidine 5'-monophosphate decarboxylase (OMPDC) from Saccharomyces cerevisiae, Methanothermobacter thermautotrophicus, and Escherichia coli. This unitary PIE eliminates a proposed mechanism for enzyme-catalyzed decarboxylation in which proton transfer from Lys-93 to C-6 of OMP provides electrophilic push to the loss of CO(2) in a concerted reaction. We propose that the complete lack of selectivity for the reaction of solvent H and D, which is implied by the value of PIE = 1.0, is enforced by restricted C-N bond rotation

SUBMITTER: Toth K 

PROVIDER: S-EPMC2876347 | biostudies-literature | 2010 May

REPOSITORIES: biostudies-literature