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 (e.g., [1]). Usually the formation and reactions of these species are limited by defensive systems within cells and organisms, with these including low-molecular-mass scavengers (e.g., ascorbic acid, thiols, quinols, tocopherols, carotenoids, polyphenols, urate), enzymes that remove oxidants directly (e.g., superoxide dismutases), enzymes that remove oxidant precursors (e.g., peroxiredoxins, glutathione peroxidases, and catalases that remove peroxides), and enzyme systems that repair or remove damaged materials (methionine sulfoxide reductases, disulfide reductases/isomerases, sulfiredoxins, proteasomes, lysosomes, proteases, phospholipases, DNA repair enzymes) [1].