Antioxidants – Types and Functions

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  •  Compounds that protect our body against the toxic effect of free radicals
  • Also known as Scavengers of Free Radicals
  • Antioxidants can be classified in various ways:-(Switch to Landscape Mode if viewing this on smartphone)
    • OTBO Lipid Peroxidation:-
      • Preventive Antioxidants which block the initial production of free radicals. Eg. Catalase, glutathione peroxidase
      • Chain Breaking antioxidants which inhibit the propagative phase of liquid peroxidation. Eg., Vitamin E, Superoxide dismutase(SOD)
    • OTBO Location:-
      • Plasma antioxidants- Eg., beta-carotene, ceruloplasmin, etc.
      • Cell membrane antioxidants: alpha tocopherol
      • Intracellular antioxidants- SOD, glutathione peroxidase, catalase.
    • OTBO Nature and action-
      • Enzymatic- Also called scavenger enzymes. Eg., SOD, Catalase, Glutathione Peroxidase
      • Nonenzymatic:-
        • Nutrient Antioxidants:-
          • Vitamins antioxidants: Vitamin E(tocopherol), Vitamin A(beta-carotene). Vitamin C(Ascorbic Acid)
          • Mineral antioxidants: Mn, Cu, Zn, Se.
        • Metabolic Antioxidants-
          • Glutathione, Ceruloplasmin, Albumin, Bilirubin, etc
  • SOD-
    • First line of defense against oxidant activity of superoxide
    • Has 2 isomers SOD 1 and SOD 2
    • SOD 1 is the cytosolic part with Cu and Zn containing enzymes
    • SOD 2 is the mitochondrial part with Mn containing enzymes
    • Converts Superoxide to hydrogen peroxide and oxygen
  • Catalase-
    • Present in peroxisomes
    • Converts the hydrogen peroxide formed by SOD to water and oxygen
  • Glutathione Peroxidase(GSH-Px)-
    • Se containing enzyme
    • Utilizes Reduced Glutathione(GSH) as reducing agent which is regenerated through Glutathione Reductase.
    • GSH-Px + GSH + Lipid Hydroperoxide  = Hydroxy fatty acids + Oxidized Glutathione(GSSG)
    • GSH + GSH-Px + Hydrogen Peroxide = Water + GSSG
  • Vitamin E-
    • Alpha tocopherol is the biologically most active form
    • Important chain breaking antioxidant which protects against lipid peroxidation
    • Lipid Peroxide radical + Reduced Vitamin E = Tocopheroxyl Radical

NB: OTBO= On The Basis of.