在自发和酶化水解中,甘酸盐与酸盐对比
Phillip M Danby1, Stephen G Withers1
1Department of Chemistry, University of British Columbia , 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada.
Journal of the American Chemical Society
|July 25, 2017
概括
酵素前和糖转移反应具有惊人的相似之处. 研究人员发现,乙烯以类似的动力学和过渡状态进行水解,这表明一种共享的酶机制.
科学领域:
- 生物化学
- 酵素学
- 有机化学
背景情况:
- 酶性前和糖转移反应产生具有多种功能的分子.
- 这两种反应类型都使用二酸激活的捐赠体,并涉及阴离子中间体.
- 酸和酸离子是这些反应中的关键酸物种.
研究的目的:
- 调查酶性 prenyl 和 glycosyl 转移之间的机制关系.
- 探索使用乙烯以模仿糖的方法.
- 为了比较解动力学和乙醇的过渡状态.
主要方法:
- 作为糖化物模拟剂的瓦利乙烯的合成.
- 测量基和乙烯的自发水解速率常数.
- 激活度,度和二次动态同位素效应 (KIEs) 的确定.
- 对β-葡萄糖酶库进行查,以检测酶活性与乙烯相对抗.
- 对选定的β-葡萄糖酶进行详细的酶分析
主要成果:
- 自发水解速率常数,激活参数和二次KIEs几乎相同.
- 对100多种β- 葡萄糖酶进行了查,其中一些具有对乙烯的催化活性 (kcat高达20s-1).
- 乙醇的酶解通过与糖化物非常相似的机制和过渡状态进行.
结论:
- 在酶化水解研究中,乙醇作为有效的糖化物仿真剂.
- 观察到的动力学和过渡状态的相似性表明这些酶反应具有共同的机制基础.
- 酶对乙烯具有催化活性,这表明乙烯和糖转移途径之间存在潜在的进化联系.
- 循环醇乙烯的较低酶分裂率可能来自酶专业化而不是内在反应性差异.
相关概念视频
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
9.8K
The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
9.8K
01:13Esters to Carboxylic Acids: Acid-Catalyzed Hydrolysis
4.2K
Hydrolysis of esters under acidic conditions proceeds through a nucleophilic acyl substitution. In the presence of excess water, the reaction proceeds in a reversible manner, forming carboxylic acids and alcohols.
During hydrolysis, the ester is first activated towards nucleophilic attack through the protonation of the carboxyl oxygen atom by the acid catalyst. The protonation makes the ester carbonyl carbon more electrophilic. In the next step, water acts as a nucleophile and adds to the...
During hydrolysis, the ester is first activated towards nucleophilic attack through the protonation of the carboxyl oxygen atom by the acid catalyst. The protonation makes the ester carbonyl carbon more electrophilic. In the next step, water acts as a nucleophile and adds to the...
4.2K
01:18π Molecular Orbitals of the Allyl Cation and Anion
5.7K
An allyl group is a three-carbon conjugated system where the sp³-hybridized allylic carbon is bonded to a CH=CH2 group via a single bond. Allyl anions can be obtained by treating propene with a strong base that can deprotonate methyl groups. Allyl cations are formed as intermediates during substitution reactions involving allylic halides. In both cases, the hybridization of the allylic carbon changes from sp3 to sp2, giving rise to a carbon chain with three sp2-hybridized carbons, each with...
5.7K
02:40Alkynes to Aldehydes and Ketones: Acid-Catalyzed Hydration
11.1K
Introduction
Analogous to alkenes, alkynes also undergo acid-catalyzed hydration. While the addition of water to an alkene gives an alcohol, hydration of alkynes produces different products such as aldehydes and ketones.
Analogous to alkenes, alkynes also undergo acid-catalyzed hydration. While the addition of water to an alkene gives an alcohol, hydration of alkynes produces different products such as aldehydes and ketones.
11.1K
01:19Aldehydes and Ketones with Alcohols: Hemiacetal Formation
10.2K
Similar to water, alcohols can add to the carbonyl carbon of the aldehydes and ketones. The addition of one molecule of alcohol to the carbonyl compound forms the hemiacetal or half acetal. As depicted below, in a hemiacetal, the carbon is directly linked to an OH and OR group.
10.2K
01:23Reactivity of Enolate Ions
3.4K
Enolate ions are formed by the acid–base reaction of a carbonyl compound with a base. This leads to deprotonation of the α hydrogen atom, leading to a resonance-stabilized enolate ion where one of the contributing structures is an oxyanion, which imparts additional stability. Therefore, the proton on the α carbon is more acidic in nature than that of other sp3-hybridized C–H bonds but less acidic than those in O–H bonds where the negative charge in the conjugate...
3.4K