Mechanistic insights from reaction of α-oxiranyl-aldehydes with cyanobacterial aldehyde deformylating oxygenase.
Mechanistic insights from reaction of α-oxiranyl-aldehydes with cyanobacterial aldehyde deformylating oxygenase.
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DOI：
10.1021/cb400772q
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发表时间：
2014-02-21
影响因子：
4
通讯作者：
Marsh, E. Neil G.
中科院分区：
文献类型：
--
作者：
Das, Debasis;Ellington, Benjamin;Paul, Bishwajit;Marsh, E. Neil G.
由脂肪酸衍生的长链脂肪烃的生物合成在自然界中广泛存在。该途径的最后一步涉及脂肪醛脱羰成相应的烷烃或烯烃。在蓝细菌中，这是由醛脱甲酰加氧酶催化的。我们已经研究了这种酶的机制，使用基板轴承环氧乙烷环相邻的醛碳。该酶催化这些底物的脱氨以产生相应的环氧乙烷。在D2 O中进行反应允许通过1H-NMR光谱检查质子加成的面选择性。质子以相等的概率传递到环氧乙烷环的任一面，表明在反应期间形成自由旋转的环氧乙烷基中间体。出乎意料的是，这种酶还催化一种副反应，在这种副反应中，环氧乙烷醛进行串联脱乙酰，以提供短两个碳的烷烃。我们提出的证据表明，这涉及的中间体环氧乙烷基自由基在第一步中形成的重排，导致醛，在第二步中进一步脱甲酰化。这些观察结果提供了支持的自由基的机制去氧杂环丁烷，而且，允许自由基中间体的寿命估计的基础上事先测量的环氧乙烷基的重排速率常数。
The biosynthesis of long-chain aliphatic hydrocarbons, which are derived from fatty acids, is widespread in Nature. The last step in this pathway involves the decarbonylation of fatty aldehydes to the corresponding alkanes or alkenes. In cyanobacteria this is catalyzed by an aldehyde deformylating oxygenase. We have investigated the mechanism of this enzyme using substrates bearing an oxirane ring adjacent to the aldehyde carbon. The enzyme catalyzed the deformylation of these substrates to produce the corresponding oxiranes. Performing the reaction in D2O allowed the facial selectivity of proton addition to be examined by 1H-NMR spectroscopy. The proton is delivered with equal probability to either face of the oxirane ring, indicating the formation of an oxiranyl radical intermediate that is free to rotate during the reaction. Unexpectedly, the enzyme also catalyzes a side reaction in which oxiranyl-aldehydes undergo tandem deformylation to furnish alkanes two carbons shorter. We present evidence that this involves the rearrangement of the intermediate oxiranyl radical formed in the first step, resulting an aldehyde that is further deformylated in a second step. These observations provide support for a radical mechanism for deformylation and, furthermore, allow the lifetime of the radical intermediate to be estimated based on prior measurements of rate constants for the rearrangement of oxiranyl radicals.
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影响因子：
2.9
作者：
Li, Ning;Chang, Wei-chen;Bollinger, J. Martin, Jr.
通讯作者：
Bollinger, J. Martin, Jr.
影响因子：
3.6
作者：
PADWA, A;DAS, NC
通讯作者：
DAS, NC
影响因子：
1.8
作者：
ITZEL, H;FISCHER, H
通讯作者：
FISCHER, H
影响因子：
11.6
作者：
Aarts, MGM;Keijzer, CJ;Pereira, A
通讯作者：
Pereira, A
影响因子：
2.9
作者：
Eser, Bekir E.;Das, Debasis;Han, Jaehong;Jones, Patrik R.;Marsh, E. Neil G.
通讯作者：
Marsh, E. Neil G.