Biochemical mechanisms accounting for the toxic action of oxygen on living organisms: The key role of superoxide dismutase

It seems that Superoxide dismutase plays the key role in protecting aerobes against O2 toxicity, but there is a whole range of ancillary mechanisms; enzymes to remove H202 (catalase, peroxidases) and hence to control formation of ·OH from 02, which requires H202; antioxidants (ascorbate, GSH, α-tocopherol, carotenoids), which also react with singlet oxygen and/or ·OH and often inhibit lipid peroxidation and last, but not least in animals, glutathione peroxidase, which controls the rate of lipid peroxidation. These mechanisms cope well at normal 02 concentrations but are insufficient at higher levels.