title: Mechanism of inhibition and decoupling of oxygen evolution from electron transfer in photosystem II by fluoride, ammonia and acetate.
abstract: Ca(2+) extraction from oxygen-evolving complex (OEC) of photosystem II (PSII) is accompanied by decoupling of oxygen evolution/electron transfer processes [Semin et al. Photosynth. Res. 98 (2008) 235] and appearance of a broad EPR signal at g=2 (split "S3" signal) what can imply the relationship between these effects. Split signal have been observed not only in Ca-depleted PSII but also in PSII membranes treated by fluoride anions, sodium acetate, and NH4Cl. Here we investigated the question: can such compounds induce the decoupling effect during treatment of PSII like Ca(2+) extraction does? We found that F(-), sodium acetate, and NH4Cl inhibit O2 evolution in PSII membranes more effectively than the reduction of artificial electron acceptor 2,6-dichlorophenolindophenol, i.e. the action of these compounds is accompanied by decoupling of these processes in OEC. Similarity of effects observed after Ca(2+) extraction and F(-), CH3COO(-) or NH4Cl treatments suggests that these compounds can inactivate function of Ca(2+). Such inactivation could originate from disturbance of the network of functionally active hydrogen bonds around OEC formed with participation of Ca(2+). This inhibition effect is observed in the region of low concentration of inhibitors. Increasing of inhibitor concentration is accompanied by appearance of other sites of inhibition.
authors.affiliation: Department of Biophysics, Faculty of Biology, Lomonosov Moscow State University, 119234 Moscow, Russia.
authors.forename: E R
authors.initials: ER
authors.lastname: Lovyagina
authors.affiliation: Department of Biophysics, Faculty of Biology, Lomonosov Moscow State University, 119234 Moscow, Russia. Electronic address: semin@biophys.msu.ru.
authors.forename: B K
authors.initials: BK
authors.lastname: Semin
mesh_terms: D000085:Acetates / Q000737:chemistry*; D000641:Ammonia / Q000737:chemistry*; D004579:Electron Transport; D005453:Fluorescence; D005459:Fluorides / Q000737:chemistry*; D007700:Kinetics; D010100:Oxygen / Q000737:chemistry*; D045332:Photosystem II Protein Complex / Q000378:metabolism*
chemical_list: D000085:Acetates; D045332:Photosystem II Protein Complex; D000641:Ammonia; D005459:Fluorides; D010100:Oxygen
keywords: Acetate; Ammonia; Calcium; Chloride; Fluoride; Oxygen-evolving complex