Superoxide dismutase hydrogen peroxide production

ROS generation is generally a cascade of reactions that starts with the production of superoxide. Superoxide rapidly dismutates to hydrogen peroxide either spontaneously, particularly at low pH, or catalyzed by superoxide dismutase (SOD). 

The production of active oxygen species may lead to a cycle of oxidation and reduction (redox cycle) with electrons being donated to oxygen to yield superoxide. This is the case with paraquat and also a number of cytotoxic quinones. Thus, there is a cyclic process, which produces superoxide by adding electrons from paraquat (see chap. 7) or a semiquinone, for example, to oxygen (Fig. 6.10). The superoxide produced may then be metabolized to hydrogen peroxide by superoxide dismutase, which is further metabolized to water by catalase (Fig. 6.10). 

However, the superoxide dismutase may be overwhelmed by the amount of superoxide being produced after a toxic dose of paraquat. The superoxide may then cause lipid peroxidation via the production of hydroxyl radicals. These may be produced from hydrogen peroxide in the presence of transition metal ions (see chap. 6). 

The reaction products of superoxide ions are believed to be partly responsible for the removal and destruction of bacteria and damaged cells [1]. In view of its low reactivity it is unlikely that superoxide itself is responsible for killing the invading material, but the hydrogen peroxide formed from dismutation by superoxide dismutase can kill some strains of bacteria. Once the phagocytic... 

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