氧酸盐,酸,乙酸和酸脱碳酶面临的动力挑战
Richard Wolfenden1, Charles A Lewis, Yang Yuan
1Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599-7260, United States. water@med.unc.edu
Journal of the American Chemical Society
|March 26, 2011
概括
酶极大地加速反应. 未催化氧沙酸脱碳化是极其缓慢的,显示像氧沙酸脱碳化酶这样的酶为生物过程提供了巨大的速度增强.
科学领域:
- 生物化学 生物化学
- 酶动力学 酶动力学
- 化学反应的速度 化学反应的速度
背景情况:
- 酶作为生物催化剂,显著增加反应速率.
- 了解未催化反应对于量化酶效率至关重要.
研究的目的:
- 为了比较酶的催化功率与未催化反应.
- 为了确定由氧酸盐脱碳酶提供的速率提升.
主要方法:
- 确定在高温下对阿里法酸的未催化脱碳化速率.
- 将反应速率推算到25°C的标准温度.
- 研究辅助因子 (O(2),Mn(II)) 对反应机制的影响.
主要成果:
- 在pH4.2下,氧沙酸的未催化脱碳化速率为1.1 × 10(-12) s(-1).
- 氧沙酸脱碳酶提供了估计的2.5 × 10 13 倍的增速.
- 未催化氧沙酸脱碳化是独立于O2和Mn2的,这表明异质消除.
结论:
- 与未催化反应相比,酶可以显著提高速率.
- 在未催化和酶催化时,氧沙酸脱碳化通过不同的机制进行.
相关概念视频
01:02Loss of Carboxy Group as CO2: Decarboxylation of β-Ketoacids
Carboxylic acids, upon heating, undergo a decarboxylation reaction by releasing carbon dioxide gas. Monocarboxylic acids do not undergo decarboxylation easily. However, a silver salt of carboxylic acid reacts with bromine or iodine under high temperature to release carbon dioxide gas and forms halide with one less carbon. This reaction is called the Hunsdiecker reaction.
01:35Loss of Carboxy Group as CO2: Decarboxylation of Malonic Acid Derivatives
Just like β-keto acids—which upon thermal decarboxylation form ketones—β-dicarboxylic acids undergo decarboxylation to generate monocarboxylic acids with the liberation of carbon dioxide.
01:15Oxidations of Aldehydes and Ketones to Carboxylic Acids
Oxidation of aldehydes and ketones results in the formation of carboxylic acids. Aldehydes, bearing hydrogen next to the carbonyl group, are easily oxidized compared to ketones. This is because an aldehydic proton can easily be abstracted during oxidation.
Aldehydes readily undergo oxidation in strong oxidizing agents such as potassium permanganate and chromic acid. The oxidation can also be carried out using mild oxidizing agents such as silver oxide. In fact, aldehydes can be easily oxidized...
Aldehydes readily undergo oxidation in strong oxidizing agents such as potassium permanganate and chromic acid. The oxidation can also be carried out using mild oxidizing agents such as silver oxide. In fact, aldehydes can be easily oxidized...
01:15Pyruvate Oxidation
After glycolysis, the charged pyruvate molecules enter the mitochondria via active transport and undergo three enzymatic reactions. These reactions ensure that pyruvate can enter the next metabolic pathway so that energy stored in the pyruvate molecules can be harnessed by the cells.
First, the enzyme pyruvate dehydrogenase removes the carboxyl group from pyruvate and releases it as carbon dioxide. The stripped molecule is then oxidized and releases electrons, which are then picked up by NAD+...
First, the enzyme pyruvate dehydrogenase removes the carboxyl group from pyruvate and releases it as carbon dioxide. The stripped molecule is then oxidized and releases electrons, which are then picked up by NAD+...
01:14Alkylation of β-Diester Enolates: Malonic Ester Synthesis
Malonic ester synthesis is a method to obtain α substituted carboxylic acids from ꞵ-diesters such as diethyl malonate and alkyl halides.
01:22Reactions of Aldehydes and Ketones: Baeyer–Villiger Oxidation
Baeyer–Villiger oxidation converts aldehydes to carboxylic acids and ketones to esters. The reaction uses peroxy acids or peracids and is often catalyzed by acid. The reaction is named after its pioneers, Adolf von Baeyer and Victor Villiger. The reaction is achieved by a wide range of peracids such as m-chloroperoxybenzoic acid (mCPBA), perbenzoic acid (C6H5COOOH), peracetic acid (CH3COOOH), hydrogen peroxide (H2O2), and tert-butyl hydroperoxide (t-BuOOH).
The carbonyl center is activated by...
The carbonyl center is activated by...