ABSTRACT
Biological systems are continually exposed to endogenous and exogenous free radicals and two-electron oxidants. The processes that give rise to these species have been reviewed. Usually the formation and reactions of these species are limited by defensive systems within cells and organisms, with these including low-molecular-mass scavengers, enzymes that remove oxidants directly, enzymes that remove oxidant precursors, and enzyme systems that repair or remove damaged materials. Many oxidant reactions give rise to secondary oxidants, of different reactivity and lifetimes than the initial species, further complicating the analysis of damage. This focuses on the role of peroxides as initiators, intermediates, and products of protein modification. As most oxidants react with multiple targets, there is the possibility of damage to all major classes of biological molecules. Peroxides can act as both direct and indirect initiating agents in protein damage.
