The enzymatic antioxidants are (a) catalase and the various peroxidases, whose presence lowers the concentration of hydrogen peroxide, thereby preventing it from entering into potentially damaging reactions with various cell components (see Section VI and Reactions 5.82 and 5.83), and (b) the superoxide dismutases, whose presence provides protection against dioxygen toxicity that is believed to be mediated by the superoxide anion, O2 - (see Section VII and Reaction 5.95).
Some of the enzymatic and nonenzymatic antioxidants in the cell are illustrated in Figure 5. I.
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