Sétif P, Ikegami I, Biggins J
Département de Biologie, C.E.N. Saclay, Gif-sur-Yvette, France.
Biochim Biophys Acta. 1987 Nov 19;894(2):146-56. doi: 10.1016/0005-2728(87)90184-8.
The photoreduction of iron-sulfur centers was studied at low temperature in Photosystem I particles from spinach and the cyanobacterium Synechocystis 6803, which contain various amounts of vitamin K-1 (recently tentatively identified as the acceptor A1). The irreversible charge separation that was progressively induced at low temperature between P-700 and FA (or FB) by successive laser flashes was studied at 15 K. Its maximum amount after a large number of flashes was shown to be fairly independent of the number (0, 1 or 2) of vitamins K-1 per reaction center. Moreover, the first flash yield of this charge separation was diminished by only about 50% when vitamin K-1 was completely absent from the particles by comparison with particles containing one or two vitamin K-1 per reaction center. When FA and FB were prereduced, the iron-sulfur center FX was also reversibly photoreduced at 9 K in the absence of vitamin K-1. The implications of these results for the electron pathways of Photosystem I are discussed and it is proposed that a direct electron transfer from A0- to the iron-sulfur centers is highly efficient at low temperature.
在菠菜和蓝藻集胞藻6803的光系统I颗粒中，对铁硫中心的光还原进行了低温研究，这些颗粒含有不同量的维生素K-1（最近初步鉴定为受体A1）。在15K下研究了通过连续激光闪光在低温下P-700与FA（或FB）之间逐步诱导的不可逆电荷分离。大量闪光后其最大量显示与每个反应中心维生素K-1的数量（0、1或2）相当无关。此外，与每个反应中心含有一个或两个维生素K-1的颗粒相比，当颗粒中完全不存在维生素K-1时，这种电荷分离的首次闪光产率仅降低约50%。当FA和FB被预还原时，在没有维生素K-1的情况下，铁硫中心FX在9K时也会被可逆地光还原。讨论了这些结果对光系统I电子途径的影响，并提出从A0-到铁硫中心的直接电子转移在低温下效率很高。
