Nh

Figure 9.3. Scheme 1.

Figure 9.3. Scheme 1.

oxidized proteins (Dukan and Nyström, 1999; Nyström, 2002; Aguilaniu et al., 2001; Ballesteros et al., 2001). Experiments with growth-arrested Escherichia coli demonstrated that protein carbonylation is fairly selective to specific proteins. Misfolded proteins are especially susceptible to the formation of protein-associated carbo-nyls (Dukan et al., 2000). Mechanistically, not the rate of respiration per se but the degree of coupling in the mitochondrial respiratory apparatus appears to be responsible for the increased accumulation of oxidized proteins (Aguilaniu et al., 2001). A remarkable observation was that mother cells retain a large fraction of oxidized proteins during cell division, somehow protecting their daughter cells from the consequences of protein oxidation (Aguilaniu et al., 2003). Such a result would suggest that old tissues would have a reduced ability to resist oxidative stress; however, recently experiments with Arabidopsis thaliana demonstrated a mechanism in plants, where old leaves can eliminate oxidized proteins prior to bolting and flowering of the plant (prior to reproduction) (Johansson et al., 2004).

Predominantly Western blot analysis demonstrated a quite selective age-dependent accumulation of carbonyl-ated proteins in Drosophila melanogaster (Das et al., 2001) and human Alzheimer's disease brain (Castegna et al., 2002a; 2002b). Selective protein carbonyl-association was also detected in the brain of SAMP8 mice (Poon et al., 2004) and model experiments where the Alzheimer's disease ^-amyloid peptide was directly injected into rat brain (Boyd-Kimball et al., 2005). However, all these Western blot-based experiments identified only a small subset of carbonylated proteins compared to the more than 100 carbonyl-containing proteins identified in brain via a complementary approach, where proteins were derivatized with a biotin-containing hydrazide, and the so biotinylated proteins immunoenriched with immobilized streptavidin (Soreghan et al., 2003). An important

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