Beckman, Kenneth B., and Bruce N. Ames. The Free Radical Theory of Aging Matures. Physiol. Rev. 78: 547–581, 1998. — The free radical theory of aging, conceived in 1956, has turned 40 and is rapidl...

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The Free Radical Theory of Aging Matures

The imposition of oxidative stress leads to increased production of reactive oxygen species (ROS) in plant cells. Orchestrated defense processes ensue that have much in common between stresses, yet are also particular to the site of action of the stress and its concentration. Possible functional roles of these responses include, but are not restricted to, the protection of the photosynthetic machinery, the preservation of membrane integrity and the protection of DNA and proteins. Superimposed upon our understanding of cellular mechanisms for protection against abiotic stress is a newly discovered role of ROS in signalling and defense response to pathogens (J. L. Dangl, R. A. Dietrich and M. S. Richberg. 1996. Plant Cell 8: 1793–1807). Evidence to date suggests a coordinated response to ROS among different members of the superoxide dismutase (SOD) gene families. A further layer of complexity is afforded by reports of coordination of expression between ascorbate peroxidase and SOD genes. Our understanding of the signalling mechanisms that underlie these coordinated events is in its infancy. An exciting future lies ahead in which the orchestration of successful antioxidant stress responses will be gradually revealed. Current data suggest that complex regulatory mechanisms function at both the gene and protein level to coordinate antioxidant responses and that a critical role is played by organellar localization and inter-compartment coordination.

Reactive oxygen species and antioxidants: Relationships in green cells

Degradation of oxidized proteins by the 20S proteasome.

Protein oxidation in vivo is a natural consequence of aerobic life. Oxygen radicals and other activated oxygen species generated as by-products of cellular metabolism or from environmental sources cause modifications to the amino acids of proteins that generally result in loss of protein function/enzymatic activity. Oxidatively modified proteins can undergo direct chemical fragmentation or can form large aggregates due to covalent cross-linking reactions and increased surface hydrophobicity. Mammalian cells exhibit only limited direct repair mechanisms and most oxidized proteins undergo selective proteolysis. The proteasome appears to be largely responsible for the degradation of soluble intracellular proteins. In most cells, oxidized proteins are cleaved in an ATP-and ubiquitin-independent pathway by the 20 S "core" proteasome. The proteasome complex recognizes hydrophobic amino acid residues, aromatic residues, and bulky aliphatic residues that are exposed during the oxidative rearrangement of secondary and tertiary protein structure: increased surface hydrophobicity is a feature common to all oxidized proteins so far tested. The recognition of such (normally shielded) hydrophobic residues is the suggested mechanism by which proteasome catalyzes the selective removal of oxidatively modified cell proteins. By minimizing protein aggregation and cross-linking and by removing potentially toxic protein fragments, proteasome plays a key role in the overall antioxidant defenses that minimize the ravages of aging and disease.

Degradation of oxidized proteins in mammalian cells.

Oxidative stress in skin plays a major role in the aging process. This is true for intrinsic aging and even more for extrinsic aging. Although the results are quite different in dermis and epidermis, extrinsic aging is driven to a large extent by oxidative stress caused by UV irradiation. In this review the overall effects of oxidative stress are discussed as well as the sources of ROS including the mitochondrial ETC, peroxisomal and ER localized proteins, the Fenton reaction, and such enzymes as cyclooxygenases, lipoxygenases, xanthine oxidases, and NADPH oxidases. Furthermore, the defense mechanisms against oxidative stress ranging from enzymes like superoxide dismutases, catalases, peroxiredoxins, and GSH peroxidases to organic compounds such as L-ascorbate, α-tocopherol, beta-carotene, uric acid, CoQ10, and glutathione are described in more detail. In addition the oxidative stress induced modifications caused to proteins, lipids and DNA are discussed. Finally age-related changes of the skin are also a topic of this review. They include a disruption of the epidermal calcium gradient in old skin with an accompanying change in the composition of the cornified envelope. This modified cornified envelope also leads to an altered anti-oxidative capacity and a reduced barrier function of the epidermis.

/pdf/oxidative-stress-in-aging-human-skin-3ohc7c9zri.pdf

Oxidative Stress in Aging Human Skin

Hydrophobicity as the signal for selective degradation of hydroxyl radical-modified hemoglobin by the multicatalytic proteinase complex, proteasome.

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Hydrophobicity as the signal for selective degradation of hydroxyl radical-modified hemoglobin by the multicatalytic proteinase complex, proteasome.