HYDROPEROXIDE METABOLISM IN MAMMALIAN ORGANS

The cell employs several lines of defense against the toxic products of oxygen reduction. The first is systemic protection against high oxygen tensions at the cellular level. The second is the intracellular localization of the enzymes appropriate to the decomposition of the toxic intermediates at or near the site where they are generated, together with steep gradients of the reactive species themselves. A third line of defense is provided by radical scavengers such as α-tocopherol and β-carotene, which also have the advantage of being appropriately distributed in the membranes where lipid peroxidation might occur. A fourth level of protection is provided by glutathione peroxidase, which reacts directly with lipid peroxides. Finally, recent understanding of the beneficial action of H(2)O(2) in phagocytosis and in ethanol oxidation suggests caution in condemning any metabolite as useless until its functions in toto are thoroughly understood.