Free-radical reaction in biological systems.

Free radicals are a highly reactive chemical species which differ from all other species in possessing an unpaired electron. Although free-radical activity in living systems is energetically improbable, recent work suggests that a number of important biological processes depend on it. In contrast to enzymic metabolism these free-radical processes tend to be non-cyclic, irreversible, non-homoeostatic, and energetically wasteful. For the organism as a whole they may nevertheless have considerable survival value. Free radicals are too short-lived to be demonstrable in tissues; but methodological advances are leading to the detection and measurement of characteristic free-radical reaction products. The findings suggest that free-radical activity is not only a potential cause but also a common, perhaps invariable, consequence of cell damage. It is possible that some of the secondary products of free-radical reactions may help to regulate the body's local and systemic response to injury.