Oxygen radicals, oxygen toxicity and the life of microorganisms.

Resumo

The electronic structure of dioxygen in the ground state dictates that its reduction occur most easily by a univalent pathway which involves the dangerously reactive intermediates 0₂-, H₂0₂ and OH. The oxygenation of earth’s biosphere 3.5 x 10⁹ years ago provided both opportunity and threat. The opportunity to exploit oxygen for energy-yielding and biosynthetically useful oxidations has been seized, as evidenced by the abundant and predominantly aerobic flora and fauna of this planet. At the same time the threat has been largely neutralized by a variety of defensive strategies. The superoxide dismutases are an important part of this defense against oxygen toxicity. Much of the research on superoxide dismutase has been done with microorganisms, due to their flexibility as laboratory tools and because there appears to be close similarity between oxygen toxicity threat and defense in microorganisms and in higher organisms. Data resulting from this work appear to have application in understanding a number of basic biological and medical phenomena, in particular the mechanisms of hyperbaric oxygen toxicity, anoxic tissue damage, anaerobiosis, oxidative damage in aging and mutagenesis, inflammation, phagocytosis, and the pharmacology of certain antitumor drugs and antibiotics. In each of these areas, whether the role of 0₂- and the other oxygen species ultimately proves to be major or minor, beneficial or harmful, application of the concept of oxygen toxicity to experimental design is resulting in a substantial improvement in our understanding of the mechanisms involved.