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
复制标题
DOI：
10.1021/ja076222f
复制
发表时间：
2007-10-31
影响因子：
15
通讯作者：
Richard, John P.
中科院分区：
文献类型：
--
作者：
Toth, Krisztina;Amyes, Tina L.;Richard, John P.
乳清酸核苷5 '-单磷酸脱羧酶催化乳清酸核苷5'-单磷酸（OMP）在50/50（v/v）H_2O/D_2O中脱羧，[6-H-1]-尿苷5 '-单磷酸（50%）和[6-H-2]-尿苷5'-单磷酸（50%）的产率之比为1.0。这种单一产物同位素效应消除了酶催化脱羧的提出机制，其中质子从Lys-93转移到OMP的C-6提供了协同反应中CO2损失的亲电推动。由PIE = 1.0的值暗示的溶剂H和D的反应的选择性的完全缺乏可以通过已经提出质子化乙烯基碳负离子中间体的Lys-93的侧链的NL 3+基团的受限运动来加强。
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.