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9.1B: What is an Antioxidant?

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    1510
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    We are ready to move on to antioxidants, which as their name indicates, combat free radicals, ROS, and oxidative stress. You have probably heard the saying "take one for the team." Instead of taking one for the team, antioxidants "give one for the team." The ‘giving’ is the donation of an electron from the antioxidant to a free radical, in order to regenerate a stable compound, as shown below.

    Figure 9.121 .png

    Figure 9.121 Regeneration of normal oxygen from oxygen free radical by the donation of an electron from an antioxidant

    Donating an electron is how vitamins act as antioxidants. Minerals, on the other hand, are not antioxidants themselves. Instead, they are cofactors for antioxidant enzymes. These antioxidant enzymes include:

    • Superoxide dismutase (SOD): uses copper, zinc, and manganese as cofactors (there is more than one SOD enzyme); converts superoxide to hydrogen peroxide and oxygen1.
    • Catalase: uses iron as a cofactor; converts hydrogen peroxide to water1.
    • Glutathione peroxidase (GPX): is a selenoenzyme that converts hydrogen peroxide to water. It can also convert other reactive oxygen species (ROSs) to water1.

    The action of these enzymes is shown below.

    Figure 9.122.png

    Figure 9.122: Antioxidant enzymes that use minerals as cofactors

    Antioxidants are thought to work in concert with one another, forming what is known as the antioxidant network. An example of the antioxidant network is shown below. Alpha-tocopherol (major form of vitamin E in our body) is oxidized, forming an alpha-tocopherol radical. This donation of an electron stabilizes reactive oxygen species. Ascorbate (vitamin C) is then oxidized, forming dehydroascorbate to regenerate (reduce) alpha-tocopherol. Ascorbate is then regenerated by the selenoenzyme thioredoxin reductase. This demonstrates how antioxidants can function as a network to regenerate one another so they can continue to function as antioxidants.

    Figure 9.123.png

    Figure 9.123:The theorized antioxidant network2

    References & Links

    1. Gropper SS, Smith JL, Groff JL. (2008) Advanced nutrition and human metabolism. Belmont, CA: Wadsworth Publishing.
    2. Packer L, Weber SU, Rimbach G. (2001) Molecular aspects of alpha-tocotrienol antioxidant action and cell signalling. J Nutr 131(2): 369S-373S.
    3. Auntie Oxidant - www.ibiblio.org/Dave/Dr-Fun/d...df20000523.jpg

    This page titled 9.1B: What is an Antioxidant? is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Brian Lindshield via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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