Kim S T, Heelis P F, Sancar A
Department of Biochemistry and Biophysics, University of North Carolina School of Medicine, Chapel Hill 27599.
Biochemistry. 1992 Nov 17;31(45):11244-8. doi: 10.1021/bi00160a040.
DNA photolyases catalyze the photocycloreversion of cyclobutane pyrimidine dimers. The enzyme from the cyanobacterium Anacystis nidulans contains two chromophores, 1,5-dihydroflavin adenine dinucleotide (FADH2) and 7,8-didemethyl-8-hydroxy-5-deazariboflavin (8-HDF). The photophysical/photochemical reactions leading to DNA repair were investigated by using time-resolved and steady-state fluorescence spectroscopy. It was found that the excited singlet state of 8-HDF transfers energy to FADH2 at a rate of 1.9 x 10(10) s-1 and a quantum yield of 0.98. Using the Forster equation for long-range energy transfer and assuming random orientations of the donor and acceptor the interchromophore distance was calculated to be 15 A. The excited singlet FADH2 which forms either by energy transfer from 8-HDF or by direct absorption of a photon has a lifetime of 1.8 ns in the absence of substrate and 0.14 ns in the presence of the photodimer indicating electron transfer from the FADH2 excited singlet state to the dimer at a rate of 6.5 x 10(9) s-1 and quantum efficiency of 92%.
DNA光解酶催化环丁烷嘧啶二聚体的光环化逆转反应。来自蓝细菌集胞藻6803的这种酶含有两种发色团，即1,5-二氢黄素腺嘌呤二核苷酸（FADH2）和7,8-二去甲基-8-羟基-5-去氮核黄素（8-HDF）。利用时间分辨和稳态荧光光谱研究了导致DNA修复的光物理/光化学反应。结果发现，8-HDF的激发单重态以1.9×10(10) s-1的速率和0.98的量子产率将能量转移给FADH2。使用福斯特长程能量转移方程并假设供体和受体的随机取向，计算出两个发色团之间的距离为15埃。通过从8-HDF进行能量转移或直接吸收光子形成的激发单重态FADH2，在没有底物的情况下寿命为1.8纳秒，在存在光二聚体的情况下寿命为0.14纳秒，这表明电子以6.5×10(9) s-1的速率从FADH2激发单重态转移到二聚体，量子效率为92%。
