Rigby S E, Evans M C, Heathcote P
Department of Biology, University College London, University of London, U.K.
Biochemistry. 1996 May 28;35(21):6651-6. doi: 10.1021/bi952619x.
The photoaccumulated radical state of the photosystem 1 secondary electron acceptor A1, A1.-, has been studied in spinach and the cyanobacterium Anabaena variabilis strain Met27 using electron nuclear double resonance (ENDOR) and electron--nuclear--nuclear special triple (ST) resonance spectroscopies. Spectra of A1.- in both these species are very similar. ENDOR spectra of the phylloquinone anion radical in solvent glass were also obtained. Comparison of the spectra of the in vivo and in vitro radicals shows that A1.- is a phylloquinone anion radical with a distorted electron spin density distribution. Hyperfine couplings to the A1.- methyl group and to two protons hydrogen bonded to the quinone oxygens have been identified using biosynthetic deuteration in A. variabilis. Possible hyperfine coupling to a methylene proton of the phytyl side chain of the quinone has also been identified. These results are compared with those from previous studies of protein-bound semiquinones in the light of the unusual redox potential of A1.
利用电子核双共振（ENDOR）和电子 - 核 - 核特殊三重（ST）共振光谱，对菠菜和蓝藻鱼腥藻变种Met27中光系统1二级电子受体A1的光积累自由基态A1.-进行了研究。这两个物种中A1.-的光谱非常相似。还获得了溶剂玻璃中叶醌阴离子自由基的ENDOR光谱。体内和体外自由基光谱的比较表明，A1.-是一种电子自旋密度分布扭曲的叶醌阴离子自由基。利用鱼腥藻中的生物合成氘代，已确定了与A1.-甲基以及与两个与醌氧氢键合的质子的超精细耦合。还确定了与醌的植基侧链亚甲基质子可能的超精细耦合。根据A1不寻常的氧化还原电位，将这些结果与先前关于蛋白质结合半醌的研究结果进行了比较。
