Defence against the toxic action of oxygen

Oxygen is a Yanus-faced molecule, it conditions life but it also exerts toxic effects. In the present survey, the oxygen activation, biological effects of oxygen-derived metabolites and the possible protection of living organisms have been reviewed. Superoxide and hydroxyl radicals together with hydrogen peroxide and singlet oxygen are believed to be responsible for oxygen toxicity. It is supposed that free radical mechanism is participated in inflammatory diseases, myocardial infarction, carcinogenesis, in effect of ionizing radiation or in aging. Living organisms are equipped with a variety of antioxidant agents. There are the enzymes - superoxide dismutase that dismutases superoxide radicals to hydrogen peroxide and catalase or glutathione peroxidase that detoxify hydrogen peroxide. The low molecular substances are also involved in the protection, e. g. glutathione, ascorbate, vitamins A and E. In following part of our review the knowledge on the activities of above mentioned enzymes under pathological conditions has been reported. The attention is directed to inflammation, hemolytic states, neurologic and psychiatric disorders, carcinogenesis, the effect of ionizing radiation, aging, autoimmune disease and hypoxia-reperfusion injury.