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Superoxide dismutase (SOD, ) is an enzyme that alternately catalyzes the dismutation (or partitioning) of the superoxide (O2−) radical into either ordinary molecular oxygen (O2) or hydrogen peroxide (H2O2). Superoxide is produced as a by-product of oxygen metabolism and, if not regulated, causes many types of cell damage. Hydrogen peroxide is also damaging, but less so, and is degraded by other enzymes such as catalase. Thus, SOD is an important antioxidant defense in nearly all living cells exposed to oxygen. One exception is ''Lactobacillus plantarum'' and related lactobacilli, which use a different mechanism to prevent damage from reactive (O2−). == Chemical reaction == SOD enzymes deal with the superoxide radical by alternately adding or removing an electron from the superoxide molecules it encounters, thus changing the O2− into one of two less damaging species: either molecular oxygen (O2) or hydrogen peroxide (H2O2). This SOD-catalyzed dismutation of superoxide may be written, for Cu,Zn SOD, with the following half-reactions : * Cu2+-SOD + O2− → Cu+-SOD + O2 * Cu+-SOD + O2− + 2H+ → Cu2+-SOD + H2O2 The general form, applicable to all the different metal-coordinated forms of SOD, can be written as follows: * M(n+1)+-SOD + O2− → Mn+-SOD + O2 * Mn+-SOD + O2− + 2H+ → M(n+1)+-SOD + H2O2. where M = Cu (n=1) ; Mn (n=2) ; Fe (n=2) ; Ni (n=2). In a series of such reactions, the oxidation state and the charge of the metal cation oscillates between n and n+1: +1 and +2 for Cu, or +2 and +3 for the other metals . 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「superoxide dismutase」の詳細全文を読む スポンサード リンク
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