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首页> 外文期刊>Biochemistry >Orotic Acid Decarboxylation in Water and Nonpolar Solvents: A Potential Role for Desolvation in the Action of OMP Decarboxylase
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Orotic Acid Decarboxylation in Water and Nonpolar Solvents: A Potential Role for Desolvation in the Action of OMP Decarboxylase

机译：在水和非极性溶剂中的乳清酸脱羧：脱溶剂化在OMP脱羧酶作用中的潜在作用

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摘要

ABSTRACT: OMP decarboxylase (ODCase) generates a very large rate enhancement without the assistance ofnmetals or other cofactors. The uncatalyzed decarboxylation of 1-methylorotate in water is shown to involventhe monoanion, although uncharged 1-methylorotic acid is decarboxylated at a similar rate. To measure thenextent to which the rate of the nonenzymatic decarboxylation of orotate derivatives might be enhanced byntheir removal from solvent water, the 1-phosphoribosyl moiety of OMP was replaced with 1-substituents thatnwould allow it to enter less polar solvents. When the tetrabutylammonium salt of 1-cyclohexylorotate wasntransferred from water to a series of dipolar aprotic solvents, its rate of decarboxylation increased markedly,nvarying with the relative ability of each solvent to release the substrate in the ground state from stabilizationnby solvent water acting as a proton donor. These findings are consistent with the view that separation of thensubstrate fromsolvent watermay contribute, at least to a limited extent, to the rate enhancement produced bynODCase. This enzyme’s active site, like that of another cofactorless enzyme recently shown to produce a ratenenhancement similar inmagnitude (uroporphyrinogen decarboxylase), is equipped with an ammoniumgroupnpositioned in such a way as to balance the electrostatic charge of the carboxylate group of the substrate andnlater supply a proton to the incipient carbanion in a relatively waterless environment.
机译：摘要：OMP脱羧酶（ODCase）无需金属或其他辅助因子的辅助即可产生非常大的速率增强。尽管未带电荷的1-甲基乳清酸以相似的速率脱羧，但是显示出1-甲基乳清酸酯在水中的未催化脱羧涉及单阴离子。为了测量通过从溶剂水中去除乳酸酯衍生物的非酶促脱羧反应速率的程度，将OMP的1-磷酸核糖基部分替换为1-取代基，该取代基将使其进入极性较小的溶剂。当将1-环己基原酸酯的四丁基铵盐从水中转移到一系列偶极非质子溶剂中时，其脱羧速率显着提高，这与每种溶剂通过质子水作为质子从稳定状态释放底物的相对能力无关。捐赠者。这些发现与以下观点相一致，即从溶剂水中分离底物可能至少在一定程度上促进了nODCase产生速率的提高。该酶的活性位点类似于最近被证明能产生类似放大倍数的无辅酶的活性位点（尿卟啉原脱羧酶），配有一个铵基团，以平衡底物羧酸盐基团的静电荷并随后提供质子的方式相对无水的环境中的初始碳负离子。

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  • 来源
    《Biochemistry》 |2009年第36期|p.8738-8745|共8页
  • 作者

    Charles A. Lewis Jr. and Richard Wolfenden*;

  • 作者单位

    Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599;

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