Electron transfer chain damage

Once metals have been transported to their target tissue, they need to be distributed within the subcellular compartments where they are required, and need to be safely stored when they are in excess. Nearly 90% of Fe in plants is located in the chloroplasts, where it is required in the electron transfer chain, and in the synthesis of chlorophylls, haem, and Fe—S clusters. Fe, Cu, and Zn are also required in chloroplasts as cofactors for superoxide dismutases to protect against damage by reactive oxygen species during chloroplast development, and Cu is also required in other enzymes including the essential Cu protein plastocyanin. Pathways of intracellular metal transport in plant cells are illustrated in Fig. 8.10. Transport into the chloroplast is best characterised for Cu,... 

Formation of triplet state has been observed in the RCPP complex, apparently because the extensive procedure for preparing this complex may have led to some damage of the electron-transfer chain containing the secondary acceptors. At room temperature, the lifetime of the radical pair is 20-35 ns, while the decay time of P840 is 90 /us. 

Most of the electrons donated to the mitochondrial electron transfer chain will react with oxygen to form water. However, a small percentage can leak and cause the formation of superoxide anion radicals, which, if not quickly detoxified, can lead to formation of other radicals and cause oxidative stress. Indeed the mitochondria are thought to be the main producer of ROS, which can damage proteins and nucleic acids and cause cellular damage. Mitochondria contain protective mechanisms that detoxify ROS (and so does the ceU), such as glutathione, superoxide dismutase, peroxiiedoxin, and thioredoxins, but they can be overwhelmed as an insult persists. 

Reperfusion with O2 allows recovery of oxidative phosphorylation, provided that the mitochondrial membrane has maintained some integrity and the mitochondrial transition pore can close. However, it also increases generation of free radicals. The transfer of electrons from CoQ to O2 to generate superoxide is increased. Endothelial production of superoxide by xanthine oxidase also may increase. These radicals may go on to form the hydroxyl radical, which can enhance the damage to components of the electron transport chain and mitochondrial lipids, as well as activate the... 

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