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For other uses of SOD/Sod, see Sod (disambiguation) The enzyme superoxide dismutase (SOD, ), catalyzes the dismutation of superoxide into oxygen and hydrogen peroxide. As such, it is an important antioxidant defense in nearly all cells exposed to oxygen. One of the exceedingly rare exceptions is Lactobacillus plantarum and related lactobacilli, which use a different mechanism.
Reaction A typical reaction of an SOD protein containing copper (and zinc) looks like this: In this reaction the oxidation state of the copper changes between +1 and +2. General Several common forms of SOD exist: they are proteins cofactored with copper and zinc, or manganese, iron, or nickel. Human In humans, three forms of superoxide dismutase are present. SOD1 is located in the cytoplasm, SOD2 in the mitochondria and SOD3 is extracellular. The first is a dimer (consists of two units), while the others are tetramers (four subunits). SOD1 and SOD3 contain copper and zinc, while SOD2 has manganese in its reactive centre. The genes are located on chromosomes 21, 6 and 4, respectively (21q22.1, 6q25.3 and 4p15.3-p15.1). A microtiter plate assay for SOD is available. Physiology The superoxide anion radical (O2-) spontaneously dismutes to O2 and H2O2 quite rapidly. However, SOD has the fastest turnover number (reaction rate with its substrate) of any known enzyme. In fact, its rate is diffusion-limited. Thus, under real-world intracellular conditions, SOD greatly reduces the ambient level of the dangerous superoxide radical. The presence of SOD has been shown to help protect many types of cells from the free radical damage that is important in aging, senescence, and ischemic tissue damage. SOD also helps protect cells from DNA damage, lipid peroxidation, ionizing radiation damage, protein denaturation, and many other forms of progressive cell degradation. Role in disease Mutations in the first SOD enzyme (SOD1) have been linked to familial amyotrophic lateral sclerosis (ALS, a form of motor neuron disease). The other two types have not been linked to any human diseases, however, in mice inactivation of SOD2 causes perinatal lethality and inactivation of SOD1 causes hepatocellular carcinoma. It was once believed that ALS-causing mutations to SOD1 resulted in a destabilization of the protein, and that this destabilization was the universal basis for pathogenesis. However, in 2005, this notion was dispelled when it was shown that many pathogenic variants of SOD1 are not destabilized. Cosmetic uses SOD is used in cosmetic products to reduce free radical damage to skin, for example to reduce fibrosis following radiation for breast cancer. These studies must be regarded as tenatative however, as there were not adequate controls in the study including a lack of randomization, double-blinding or placebo. See also | ||||||||
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