MECHANISMS OF ACYL AND PHOSPHORYL TRANSFER

酰基和磷酰基转移反应是本发明的基本部分。 生命系统生物化学关于其影响所知甚少 离去基团和亲核试剂，以及催化基团的影响， 这些反应的机制和过渡态。这项工作将 使用各种同位素效应研究来解决这些问题。 初步工作支持逐步机制的改变， 四面体中间体到酰基转移协同机制 具有良好离去基团的酯的反应。 的具体目标 本提案的工作是： 1.获得酰基和 在溶液中的磷酰基转移反应和酶促反应中。 这些比较将揭示酶的作用 过渡态结构上的催化基团。 2.分析机制和过渡态结构的差异， 由于离去基团和亲核试剂的变化（ 碱性或亲核性，以及连接原子的同一性， 例如，氧与硫亲核试剂）， 反应. 3.划定界限的限制一致与逐步 由亲核试剂和/或离去基团的性质确定的机理 在溶液和酶促反应中。 4.确定活化底物是否发生酶促基团转移 与未激活的反应相同的机制，或者如果机制 不同，就像它们在溶液中一样。

Acyl and phosphoryl group transfer reactions are essential parts of the biochemistry of living systems. Little is known about the influences of leaving group and nucleophile, and the effect of catalytic groups, on the mechanisms and transition states of these reactions. This work will address these questions using a variety of isotope effect studies. Preliminary work supports a change from a stepwise mechanism with a tetrahedral intermediate to a concerted mechanism for acyl transfer reactions of esters with good leaving groups. The specific goals of the work in this proposal are to: 1. Obtain detailed descriptions of the transition states for acyl and phosphoryl transfer reactions in solution and in enzymatic reactions. Comparisons of these will shed light on the effect of the enzymatic catalytic groups on transition state structure. 2. Analyze differences in mechanism and in transition state structure that arise from changes in the leaving group and in the nucleophile (changes in basicity or nucleophilicity, and in identity of the attaching atom, for example, oxygen versus sulfur nucleophiles) in solution and enzymatic reactions. 3. Delineate the boundaries of the limiting concerted vs. stepwise mechanisms as determined by properties of nucleophile and/or leaving group in the solution and in enzymatic reactions. 4. Determine whether activated substrates undergo enzymatic group transfer reactions by the same mechanisms as unactivated ones, or if the mechanisms differ, as they do in solution.