Free radicals emerge not only during normal oxygen metabolism and inflammatory processes, but also as a consequence of exposure to ionizing radiation, cigarette smoke or excessive alcohol consumption. Cellular free radicals target key organic substrates such as lipids, DNA and proteins. Protective agents and defense mechanisms act to minimize oxidative damage. This antioxidant system consists of (1) small molecules such as vitamin C and E, glutathione, carotenes and coenzyme Q, as well as (2) enzyme antioxidants which detoxify radicals or repair oxidized molecules. In aging cells and organisms, and under certain pathophysiological conditions - such as smokers’ emphysema, rheumatoid arthritis, Alzheimer’s and Parkinson’s disease - accumulation of biomolecule oxidation products indicate a disturbed balance in the oxidative stress response.
Superoxide Dismutases fight – together with Catalases - at the antioxidant forefront by detoxifying O2• radicals. In this way, these enzymes significantly decrease the free radical concentration in the cell and minimize oxidative damage. The metal-containing superoxide dismutases are located in mitochondria, the main cellular O2• production site. Decreased SOD activity may contribute to aging in cells, and mutations in the Cu/Zn-SOD are associated with neurodegenerative disease.
The side-chain sulfur of methionine is exceptionally susceptible towards oxidation, which may lead to inactivation and degradation of proteins affected. Methionine sulfoxide reductases A and B reduce the two stereoisomers of methionine sulfoxide (MetO), MetSO and MetRO, respectively, in a thioredoxin-dependent manner. Thus, they repair oxidized proteins. Since the oxidation of surface-exposed Met does not necessarily lead to inactivation, as shown for E. coli glutamine synthetase, cyclic oxidation by cellular oxidants followed by reduction by MSRs may also contribute to inactivation of free radicals.
MSRA and MSRB enzymes from Jena Bioscience constitute useful tools for oxidative stress research. Furthermore, MSRs can be utilized for the reduction of Met-containing peptides and proteins oxidized during synthesis or purification, with DTT efficiently substituting the thioredoxin system.
Also available: Antioxidant Antibodies