Fundamental aspects of reactive oxygen species, or what's the matter with oxygen?

A byproduct of normal aerobic metabolism is the generation of dangerously reactive intermediates of the reduction of O2. These include O2-, H2O2, and HO. and arise because of the predisposition of O2 for univalent reductions. These reactive oxygen species (ROS), and others that they can engender, threaten all cellular macromolecules, and defenses are needed. Among those known to date are: superoxide dismutases to convert O2- into O2 + H2O2; catalases to dismute H2O2 into O2 + H2O; and peroxidases to reduce H2O2 into 2H2O) and to reduce ROOH into ROH and H2O. These defenses are aided by enzymes that repair or recycle oxidatively damaged nucleic acids and proteins. A role for such oxidative damage in aging and neurodegenerative diseases is well supported.