Evidence for spontaneous structural changes in a dark-adapted state of photosystem II
Kelly M Halverson1, Bridgette A Barry
1Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, St. Paul, Minnesota 55108-1022, USA.
Abstract:
Photosystem II catalyzes photosynthetic water oxidation in plants, green algae, and cyanobacteria. The manganese-containing active site cycles through a series of five oxidation states, S(n), where n refers to the number of oxidizing equivalents stored. In this report, reaction-induced Fourier transform infrared and electron paramagnetic resonance spectra of the S(1)-to-S(2) transition are presented. These data suggest that changes in carboxylate ligation to manganese, changes in secondary structure, and/or changes in polarity occur during dark adaptation in the S(1) state. These spontaneous structural changes are attributed to a S(1)' intermediate, at the same oxidation level as S(1), in the process of photosynthetic water oxidation.
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