title: Evidence for spontaneous structural changes in a dark-adapted state of photosystem II.
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.
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology / Q000528:radiation effects; D003624:Darkness; D004578:Electron Spin Resonance Spectroscopy; D008345:Manganese / Q000737:chemistry*; D010084:Oxidation-Reduction / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000737:chemistry* / Q000502:physiology / Q000528:radiation effects*; D011487:Protein Conformation / Q000528:radiation effects; D013055:Spectrophotometry, Infrared; D014867:Water / Q000737:chemistry* / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D014867:Water; D008345:Manganese