Reactive species can be useful

Abstract This chapter gives examples of how oxygen radicals and other reactive species (RS) are useful. It describes how enzymes such as ribonucleotide reductase (tyrosyl, glycyl, or deoxyadenosyl radicals, the last from S-adenosylmethionine [SAM] or adenosylcobalamin), other 'radical SAM' enzymes, pyruvate formate lyase (glycyl radicals), galactose and glyoxal oxidases, and indoleamine (tyrosyl radical) or tryptophan dioxygenases use RS to bring about reactions. The roles of RS in inflammasome formation in response to damage-associated and pathogen-associated molecular patterns is described, and how RS are employed by neutrophils, macrophages, monocytes, and eosinophils to kill micro-organisms. The contributions of superoxide (generated by NADPH oxidases), hypochlorous acid, singlet O2, and peroxynitrite to killing, and the mechanisms evolved by some bacteria to resist them, are presented. Contributions of these RS to acute and chronic inflammation are detailed. The roles of NADPH oxidases and dual oxidases in other cell types (e.g. respiratory tract and gastrointestinal epithelium, lymphocytes, platelets, osteoblasts, osteoclasts, blood vessels) are described, e.g. in regulation of blood pressure and bone turnover. Involvement of RS in thyroid hormone biosynthesis, degradation of lignin, defence mechanisms of beetles, fertilization of eggs, and the defence mechanisms used by plants (e.g. the RS-generating respiratory burst oxidase homologues) against pathogens are presented. Cyclooxygenases and lipoxygenases are reviewed, in relation to the production of prostaglandins and leukotrienes in animals and its regulation by RS, as well as the roles of lipoxygenases in plants. The mechanisms of light production by green fluorescent protein and other systems (e.g. pholasin, aequorin) are described.