Intracellularly generated superoxide

As mentioned in section 3.1, uni-electron reduction of oxygen generates superoxide anions [19] and an important source are the electron-transport chains [23,27], Although components of these chains pass the bulk of electrons onto the next component of the chain some appear to leak electrons to oxygen [25]. In order to assess the level of any intracellularly generated... 

The oxygen consumed during phagocytosis is utilized by a unique enzyme system termed the respiratory burst oxidase or NADPH oxidase. The oxidase generates superoxide anion (Oj), a one-electron reduced species, driven by intracellular NADPH,... 

All aerobic organisms contain substances that help prevent injury mediated by free radicals, and these include antioxidants such as a-tocopherol and the enzymes superoxide dismutase and glutathione peroxidase. When the protective effect of the antioxidants is overwhelmed by the production of reactive oxygen species, the intracellular milieu becomes oxidative, leading to a state known as oxidative stress (Halliwell and Gutteridge, 1999). Thus the balance between the generated free radicals and the efficiency of the protective antioxidant system determines the extent of cellular damage. 

The chemical reactivity of ROS varies from the very toxic hydroxyl [ OH-] to the less reactive superoxide radical [O2-]. H2O2, althoughless reactive thanO-2, is more highly diffusible and can cross the plasma membrane. ROS inactivates membrane proteins and DNA (Berlett and Stadtman, 1997). Various processes generate ROS both extracellularly and intracellularly. ROS can directly oxidize and damage... 

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