Defense against Oxygen Toxicity

Superoxide dismutase (SOD) is a key enzyme which constitutes the first line of defense against oxygen toxicity and catalyzes the disproportionation of the superoxide anions to dioxygen and hydrogen peroxide2 ... 

M.P. Lesser, J.M. Shick (1989). Photoadaption and defenses against oxygen toxicity in zooxanthellae from natural populations of symbiotic cnidarians. J. Exp. Mar. Biol. Ecol., 134,129-141. 

Our defenses against oxygen toxicity fall into the categories of antioxidant defense enzymes, dietary and endogenous antioxidants (free radical scavengers), cellular compartmentation, metal sequestration, and repair of damaged cellular components. The antioxidant defense enzymes react with ROS and cellular products of free radical chain reactions to convert them to nontoxic products. Dietary antioxidants, such as vitamin E and flavonoids, and endogenous antioxidants, such as urate, can... 

Dutton GJ (1980) Glucuronidation of drugs and other compounds. CRC Press, Boca Raton, Florida Dykens JA (1984) Enzymic defenses against oxygen toxicity in marine cnidarians containing endo-symbiotic algae. Mar Biol Lett 5 291-301... 

DFO is known to reduce the iron-dependent generation of toxic oxygen-derived radicals during reperfusion of ischemic tissue (40). It was shown experimentally that DFO reduces the early inflammatory reaction and improves myocardial microcirculation (41). Moreover, Dross et al, (42) showed that DFO s scavenging effect on superoxide anion could play a role in the cellular defense against oxygen radicals during cardiac operation. 

Scand J Work Environ Health 12 523-537 Oberddrster G, Cox C (1990) Carcinogenicity of cadmium in animals what is the significance for man Chem Environ Toxicol 27 181-195 Ochi T, Ishiguro T, Ohsawa M (1983) Participation of active oxygen species in the induction of DNA single-strand scissions by cadmium chloride in cultured Chinese hamster cells. Mutat Res 122 169-175 Ochi T, Otsuka F, Takahashi K, Ohsawa M (1988) Glutathione and metallothioneins as cellular defense against cadmium toxicity in cultured Chinese hamster cells. Chem Biol Interact 65 1-14... 

As well as the formation of radicals, oxidative stress may also contribute to the toxicity of electrophilic metabolites. This may result from depletion by electrophiles of the glutathione pool, one of the major defenses against damage by reactive oxygen species. 

Oxygen is toxic We, whose lives depend upon a continual supply of oxygen, do not easily comprehend its toxicity. Our apparent comfort at the ambient level of oxygen is due to elaborate defenses against its very considerable toxicity. 

One of the functions of the hypophyseal-adrenocortical axis is generally considered to be a hormonal defense mechanism against a stressor. However in the presence of OHP as a stressor the hypophyseal-adrenocortical axis becomes a liability in that its increased activity augments oxygen toxicity (B12). 

As expounded above, the rise of the oxygen content of the atmosphere starting around 2.2 billion years ago created a panic among the then-living organisms. Many of them did not survive. The rise was not abrapt, and hence the organisms had chances to evolve to develop the defense mechanisms against this toxicity. 

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