Spectrally silent light induced conformation change in photosynthetic reaction centers

Spectrally silent conformation change after photo-excitation of photosynthetic reaction centers isolated from Rhodobacter sphaeroides R-26 was observed by the optical heterodyne transient grating technique. The signal showed spectrally silent structural change in photosynthetic reaction centers followed by the primary P+BPh- charge separation and this change remains even after the charge recombination. Without bound quinone to the RC, the conformation change relaxes with about 28 mu s lifetime. The presence of quinone at the primary quinone (QA) site may suppress this conformation change. However, a weak relaxation with 30-40 mu s lifetime is still observed under the presence of QA, which increases up to 40 mu s as a function of the occupancy of the secondary quinone (QB) site. (c) 2008 Federation of European Biochemical Societies. Published by Elsevier B. V. All rights reserved.