Oxygen-Evolving Complex of Chloroplast Membranes

The oxygen-evolving complex (OEC) of plants is the main energy-transforming structure of chloroplast membranes, in which the light energy is used to photosynthetically oxidize the intracellular water and to form oxygen. The conducted investigations resulted in isolating the OEC of higher plants in the functionally active state and exploring its molecular composition, photochemical properties, and structural organization. It was ascertained that OEC represents a dimer of pigment-lipoprotein complexes of photosystem 2 (PLPC PS-2) associated in a chloroplast membrane according to the mirror symmetry into an integrate structure based on hydrophobic bonds. The model was developed for the dimer structure of the complex of PS-2 that had the function of oxygen formation. This model was confirmed by the X-ray analysis of crystals of the dimer complex of PS-2 in subsequent works of a number of authors. The concept of the formation of a "hydrophobic boiler" in the area of adhesion of the reaction centers of monomeric PLPC PS-2 that determines the formation of the water-oxidizing center of the OEC was put forward based on studies of changes in the OEC functional activity under the action of stress factors. The new scheme was advanced for the two-anode organization of the water-oxidizing center as a main condition for realizing the process of the molecular oxygen formation. The mechanism of the process of photosynthetic water oxidation and molecular oxygen formation was developed on the basis of the experimental data on the structural organization of the OEC and its water-oxidizing center. The quantum-chemical modeling of the process showed its correspondence to the mechanism suggested.