The oxygen-evolving complex of chloroplast membranes

Abstract

The oxygen-evolving complex (OEC) of plants is the main energy-transforming structure of chloroplast membranes, in which light energy is used for photosynthetic oxidation of intracellular water and oxygen formation. The conducted research has resulted in isolation of functionally active OEC of higher plants and elucidation of its molecular composition, photochemical properties and structural organization. The OEC has been revealed to represent the dimer of the pigment-lipoprotein complexes of photosystem 2 (PLPC PS-2) associated in a chloroplast membrane according to the mirror symmetry rule into an integrate structure based on hydrophobic bonds. The model has been developed for the structure of the dimeric complex of PS-2 that has the function of oxygen formation. This model was confirmed by the X-ray analysis of crystals of the dimeric complex of PS-2. The concept about the fact that the “hydrophobic boiler” determining the formation of the water-oxidizing center of the OEC is formed in the area of association of the reaction centers of monomeric PLPCs PS-2 was advanced based on the regularities of change in the functional activity of the OEC under the action of stress-factors. The new scheme has been advanced for the two-anode organization of the water-oxidizing center as the main condition for realizing the process of molecular oxygen formation. The mechanism of the process of photosynthetic water oxidation and molecular oxygen formation has been developed based on the experimental data about the structural organization of the OEC and its water-oxidizing center. The quantum-chemical modeling of the process showed that its course corresponds to the mechanism suggested.