Finally, evidence for an age-related impairment of proteasome structure and function that has been reported by different groups is provided in the light of proteasomal dysfunction induced upon oxidative stress. Then, accumulation of damaged protein is presented with emphasis on the pathways implicated in the formation of altered proteins. A short description of proteasome structure and of its role in cellular functions is first given. Indeed, accumulation of altered protein can be explained by increased protein alteration, decreased protein degradation or the combination of both. One of the hypothesis put forward to explain the accumulation of altered proteins is the decrease of proteasome activity with age. The proteasome is a multi-catalytic proteolytic complex, which recognizes and selectively degrades oxidatively damaged and ubiquitinated proteins. Protein turnover is essential to preserve cell function and the main proteolytic system in charge of cytosolic protein degradation is the proteasome. Oxidized protein build up is commonly seen as a hallmark of cellular aging. Damage to macromolecules, and in particular protein, implicated in the cellular degeneration that occurs during the aging process, is corroborated by the accumulation of oxidative end-products over time.
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