Dioxygen-derived radicals in biological systems

Abstract

Three instances of the involvement of dioxygen-derived radicals in biological systems are considered. The first concerns the formation of radicals in the haemolytic reactions induced by treatment of erythrocytes by phenylhydrazine, as an example of the so-called ‘oxidant drugs’. The evidence for the formation of phenyl radicals is considered and their origin in the oxidation of phenylhydrazine by a ferryl derivative of haemoglobin postulated. The relevance to the formation of phenylated iron and porphyrin species is described. It is suspected that many instances of oxidative damage to cellular systems result from the coincidence of unsequestered redox-active metal ions (particularly those of iron and copper), reductants, and dioxygen. As an example, the damage to hepatocytes, grown in a culture medium containing cysteine, is described. The formation of radical species derived from dioxygen during the respiratory burst associated with phagocytosis is discussed. A new electrochemical method of detecting the superoxide ion produced during the respiratory burst is described. Particular emphasis is placed on the relation between the production of radical species such as the hydroxyl radical and the superoxide ion, and the extent of phagocytosis.