ABSTRACT
Oxygen is essential for life. It is used by the body in metabolic reactions to oxidize or burn foodstuffs to supply energy. However, a variety of oxidative species, free radicals (containing an unpaired electron), and excited-state substances are formed. This would include singlet oxygen (excited states epsilon and delta), superoxide ( ), hydrogen peroxide (HOOH), hydroxyl radical and certain metabolites, peroxynitrite (OONO
−), and hypochlorite (OCl
). There are probably others. In fact it has been estimated that for every 10
oxygen molecules that enter a cell, 1/100 damages protein and 1/200 damages DNA or RNA. We know lipids can be damaged as well via lipid peroxidation.
