Proteins are one of the main cellular macromolecules susceptible to oxidative modifications. One of the reasons for this consideration is the abundance of proteins in living organisms. Proteins comprise the major, non-water, component in biological systems, at the tissue, cellular or biological fluid levels. For example, in a typical plant cell, proteins represent about 30% of the total dry weight (DW), but they are between 60 and 70% of DW when the cell wall and the starch are excluded (Taiz and Zeiger 2010). Moreover, proteins are found ubiquitously in the cell, not only in soluble forms but attached to or forming part of biological membranes. On the other hand, a further indication of the importance of proteins as targets for oxidants is the rate constants for the reaction of a range of reactive radicals with proteins with respect to other biological macromolecules (Davies 2005; Xu and Chance 2007). Oxidised proteins accumulation has been considered a cause of cellular damage (Berlett and Stadtman 1997). However, considering that there are many types of protein oxidative modifications and proteins play a variety of functions in the cell, ranging from catalytic activities, structural features or regulation of several processes, it is possible to assume that protein oxidation can directly modify cell structure, signaling and metabolism.
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