Excited-state charge separation in the photochemical mechanism of the light-driven enzyme protochlorophyllide oxidoreductase.
Excited-state charge separation in the photochemical mechanism of the light-driven enzyme protochlorophyllide oxidoreductase.
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DOI：
10.1002/anie.201409881
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发表时间：
2015-01-26
期刊：
影响因子：
--
通讯作者：
Scrutton NS
中科院分区：
文献类型：
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作者：
Heyes DJ;Hardman SJ;Hedison TM;Hoeven R;Greetham GM;Towrie M;Scrutton NS
独特的光驱动酶原叶绿素氧化还原酶（POR）是了解如何利用光能驱动酶反应的重要模型系统。超快光化学过程对于捕获激发能以驱动随后的氢化物和质子转移化学至关重要，迄今为止已被证明很难检测到。我们使用了时间分辨可见光和红外光谱的组合，在皮秒-微秒时间范围内提供完整的时间分辨率，提出了光化学的新机制。活性位点残基与Pchlide分子上的羧基之间的激发态相互作用导致极化和高活性双键。这种所谓的“反应性”分子内电荷转移状态在双键上产生一个缺电子的位点，从而触发NADPH随后的亲核攻击，攻击来自烟酰胺腺嘌呤二核苷酸磷酸的带负电荷的氢化物。这项工作提供了POR中激发态过程和化学之间至关重要的缺失环节。此外，它为如何利用光能驱动酶催化和光活化化学和生物催化剂的设计提供了重要的见解。
The unique light-driven enzyme protochlorophyllide oxidoreductase (POR) is an important model system for understanding how light energy can be harnessed to power enzyme reactions. The ultrafast photochemical processes, essential for capturing the excitation energy to drive the subsequent hydride- and proton-transfer chemistry, have so far proven difficult to detect. We have used a combination of time-resolved visible and IR spectroscopy, providing complete temporal resolution over the picosecond–microsecond time range, to propose a new mechanism for the photochemistry. Excited-state interactions between active site residues and a carboxyl group on the Pchlide molecule result in a polarized and highly reactive double bond. This so-called “reactive” intramolecular charge-transfer state creates an electron-deficient site across the double bond to trigger the subsequent nucleophilic attack of NADPH, by the negatively charged hydride from nicotinamide adenine dinucleotide phosphate. This work provides the crucial, missing link between excited-state processes and chemistry in POR. Moreover, it provides important insight into how light energy can be harnessed to drive enzyme catalysis with implications for the design of light-activated chemical and biological catalysts.