Heyes Derren J, Hardman Samantha J O, Hedison Tobias M, Hoeven Robin, Greetham Greg M, Towrie Michael, Scrutton Nigel S
Manchester Institute of Biotechnology and Photon Science Institute, University of Manchester, 131 Princess Street, Manchester M1 7DN (UK).
Angew Chem Int Ed Engl. 2015 Jan 26;54(5):1512-5. doi: 10.1002/anie.201409881. Epub 2014 Dec 8.
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.
独特的光驱动酶原叶绿素酸氧化还原酶（POR）是理解如何利用光能为酶反应提供动力的重要模型系统。超快速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反应至关重要，但迄今为止，这些过程难以检测。我们结合了时间分辨可见光谱和红外光谱，在皮秒到微秒的时间范围内提供了完整的时间分辨率，从而提出了一种新的光化学机制。活性位点残基与原叶绿素酸（Pchlide）分子上的羧基之间的激发态相互作用导致形成一个极化且高反应性的双键。这种所谓的“反应性”分子内电荷转移态在双键上产生一个缺电子位点，以触发烟酰胺腺嘌呤二核苷酸磷酸（NADPH）中带负电荷的氢化物对其进行随后的亲核攻击。这项工作提供了POR中激发态过程与化学反应之间关键的缺失环节。此外，它为如何利用光能驱动酶催化提供了重要见解，这对光活化化学和生物催化剂的设计具有启示意义。
