Product Deuterium Isotope Effect for Orotidine 5'-Monophosphate Decarboxylase: Evidence for the Existence of a Short-Lived Carbanion Intermediate

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• 作者：Krisztina Toth ; Tina L. Amyes ; Bryant M. Wood ; Kui Chan ; John A. Gerlt ; John P. Richard
• 刊名：Journal of the American Chemical Society
• 出版年：2007
• 出版时间：October 31, 2007
• 年：2007
• 卷：129
• 期：43
• 页码：12946 - 12947
• 全文大小：48K
• 年卷期：v.129,no.43(October 31, 2007)
• ISSN：1520-5126

文摘

A product isotope effect (PIE) of 1.0 was obtained from the ratio of the yields of [6-¹H]-uridine 5'-monophosphate (50%) and [6-²H]-uridine 5'-monophosphate (50%) from the decarboxylation 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.