Wang Haiyu, Saxena Chaitanya, Quan Donghui, Sancar Aziz, Zhong Dongping
Departments of Physics, Chemistry, and Biochemistry, OSU Biophysics, Chemical Physics, and Biochemistry Programs, 174 West 18th Avenue, The Ohio State University, Columbus, OH 43210, USA.
J Phys Chem B. 2005 Feb 3;109(4):1329-33. doi: 10.1021/jp044652b.
We report here our femtosecond studies of the photoreduction dynamics of the neutral radical flavin (FADH) cofactor in E. coli photolyase, a process converting the inactive form to the biologically active one, a fully reduced deprotonated flavin FADH(-). The observed temporal absorption evolution revealed two initial electron-transfer reactions, occurring in 11 and 42 ps with the neighboring aromatic residues of W382 and F366, respectively. The new transient absorption, observed at 550 nm previously in photolyase, was found from the excited-state neutral radical and is probably caused by strong interactions with the adenine moiety through the flavin U-shaped configuration and the highly polar/charged surrounding residues. The solvation dynamics from the locally ordered water molecules in the active site was observed to occur in approximately 2 ps. These ultrafast ordered-water motions are critical to stabilizing the photoreduction product FADH(-) instantaneously to prevent fast charge recombination. The back electron-transfer reaction was found to occur in approximately 3 ns. This slow process, consistent with ultrafast stabilization of the catalytic cofactor, favors photoreduction in photolyase.
我们在此报告我们对大肠杆菌光解酶中中性自由基黄素（FADH）辅因子光还原动力学的飞秒研究，该过程将无活性形式转化为生物活性形式，即完全还原的去质子化黄素FADH(-)。观察到的时间吸收演化揭示了两个初始电子转移反应，分别在11皮秒和42皮秒时与W382和F366的相邻芳香族残基发生。先前在光解酶中于550纳米处观察到的新的瞬态吸收，是由激发态中性自由基产生的，可能是由于通过黄素U形构型以及高度极性/带电的周围残基与腺嘌呤部分的强相互作用所致。观察到活性位点中局部有序水分子的溶剂化动力学在大约2皮秒内发生。这些超快的有序水运动对于瞬时稳定光还原产物FADH(-)以防止快速电荷复合至关重要。发现反向电子转移反应在大约3纳秒内发生。这个缓慢的过程与催化辅因子的超快稳定一致，有利于光解酶中的光还原。
