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Product deuterium isotope effect for orotidine 5'-monophosphate decarboxylase: evidence for the existence of a short-lived carbanion intermediate



Product deuterium isotope effect for orotidine 5'-monophosphate decarboxylase: evidence for the existence of a short-lived carbanion intermediate



Journal of the American Chemical Society 129(43): 12946-7



A product isotope effect (PIE) of 1.0 was obtained from the ratio of the yields of [6-H-1]-undine 5'-monophosphate (50%) and [6-H-2]- uridine 5'-monophosphate (50%) from the decarboxytation of orotidine 5'-monophosphate (OMP) in 50/50 (v/v) H2O/D2O catalyzed by orotidine 5'-monophosphate decarboxylase. This unitary product isotope effect 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 CO2 in a concerted reaction. The complete lack of selectivity for the reaction of solvent H and D that is implied by the value of PIE = 1.0 may be enforced by restricted motion of the NL3+ group of the side-chain of Lys-93 that has been proposed to protonate a vinyl carbanion intermediate.

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Accession: 055199030

Download citation: RISBibTeXText

PMID: 17918849

DOI: 10.1021/ja076222f


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