ABSTRACT
Antioxidant networks are composed of numerous proteins, enzymes, and metabolites able to function in synchrony to ameliorate oxidative stress situations. Singlet oxygen, hydroxyl radical, peroxynitrite, and sulfenic acid are highly reactive molecules, while superoxide anion and hydrogen peroxide are less reactive. Protein oxidation is defined as the covalent modification of proteins induced or mediated by reactive oxygen species, reactive nitrogen species, or byproducts of oxidative stress. An oxidized protein can be repaired or degraded depending on the degree and type of chemical modification exerted. Proteins participating in the perception of reactive species and signal transduction have been characterized as polypeptides exhibiting high sensitivity to reversible oxidation processes, such as thiol/disulfide exchange. Inside cells, the reducing power required for all detoxifying and regenerative systems comes, directly or indirectly, from either NADPH or ferredoxin. Plants exhibit key characteristics: cells are highly compartmentalized, with the presence of plastids; two different kinds of tissues exist, performing either photosynthesis or heterotrophic metabolism.
