Antioxidant Action of Mobile Electron Carriers of the Respiratory Chain

Abstract

1.1 Evolutionary aspects Both oxidative photophosphorylation and oxidative phosphorylation are dependent on electron transport chains sharing similarities that are suggestive of evolution of a chemolithotrophy-based common ancestor (conversion hypothesis). Therefore, an early form of electron transport chain with oxidative phosphorylation that is known as prerespiration was able of donating electrons to terminal acceptors available in the primitive reducing biosphere. In the evolutionary pathway this apparatus was supplemented by a photocatalyst capable of a redox reaction. Therefore, oxygenic photosynthesis was a late event during evolution that was preceded by anoxygenic photosynthesis. The development of the manganese complex able to promote water oxidation was a key event in developing oxygenic photosynthesis (Xiong & Bauer, 2002; Bennnown, 1982; Castresanal et al., 1994). The development of oxygenic photosynthesis was one of the most important events in the biological evolution because it changed the redox balance on Earth and created conditions for the biological evolution to more complex life forms. Molecular data showing cytochrome oxidase in the common ancestor of Archaea and Bacteria and an existing cytochrome oxidase in nitrogen-fixing bacteria living in an environment where the level of oxygen was very low are indicia that aerobic metabolism could be present in an ancient organism, prior to the appearance of eubacterial oxygenic photosynthetic organisms. Although the hypothesis that aerobic metabolism arose several times in evolution after oxygenic photosynthesis is not sustained by the above mentioned data, the widespread use of molecular oxygen as final acceptor of electrons resulting from the oxidation of biological fuels was an evolutionary acquisition subsequent to the oxygen photosynthesis. The use of molecular oxygen as final acceptor of electrons removed from biological fuels resulted in a significant improvement of energy yield, a crucial event for the rise of complex heterotrophic organisms. According to the endosymbiotic theory, the respiratory chain present in prokaryotes was transferred to eukaryotes and resulted in cells bearing mitochondria. At the present step of the biological evolution, the aerobic oxidation of biological fuels occurs in the respiratory chain apparatus of the cell membrane of