MacMillan F, Hanley J, van der Weerd L, Knüpling M, Un S, Rutherford A W
Département de Biologie Cellulaire et Molécularie, CNRS URA 2096, CEA Saclay, F-91191 Gif-sur-Yvette, France.
Biochemistry. 1997 Aug 5;36(31):9297-303. doi: 10.1021/bi971097d.
The photosynthetic reaction center of photosystem I (PS I) contains a phylloquinone molecule (A1) which acts as a transient electron acceptor. In PS I form the cyanobacterium Synechocystis PCC 6803 under reducing conditions, we have photoaccumulated an EPR signal assigned to the phylloquinone radical anion. The phylloquinone EPR spectrum has been studied in oriented multilayers of PS I using EPR at 9 GHz. In addition, the phyllosemiquinone spectrum has been obtained at 283 GHz using high-field, high-frequency EPR spectroscopy. From the orientation dependence of the spectrum at 9 GHz and the resolved g values obtained at 283 GHz, the phyllosemiquinone ring plane was determined to be almost perpendicular to the membrane (76 degrees) while the oxygen-oxygen (O-O) axis of the quinone was found to make an approximate 63 degrees angle to the membrane plane. The orientation of the ring plane is similar to that determined for the quinone electron acceptor (QA) in the purple bacterial reaction center, while the orientation of the O-O axis is significantly different. The new orientation information, when taken with data in the literature, allows the position of the phylloquinone in the reaction center to be better defined.
光系统I（PS I）的光合反应中心含有一个作为瞬时电子受体的叶绿醌分子（A1）。在还原条件下，对于来自蓝细菌集胞藻PCC 6803的PS I，我们光积累了一个归属于叶绿醌自由基阴离子的电子顺磁共振（EPR）信号。利用9 GHz的EPR对PS I的定向多层膜中的叶绿醌EPR光谱进行了研究。此外，使用高场、高频EPR光谱在283 GHz处获得了半醌型叶绿醌光谱。根据9 GHz光谱的取向依赖性以及在283 GHz处获得的解析g值，确定半醌型叶绿醌的环平面几乎垂直于膜（76度），而醌的氧-氧（O-O）轴与膜平面成约63度角。环平面的取向与紫色细菌反应中心中醌电子受体（QA）的取向相似，而O-O轴的取向则明显不同。将新的取向信息与文献中的数据相结合，可以更好地确定叶绿醌在反应中心中的位置。
