Figure 1.

Pro-oxidant and antioxidant mechanisms is RBCs. O₂ binding to Hb initiates Hb auto-oxidation in which process metHb (Fe³⁺) and superoxide anion (${\text{O}}_2^{•-}$) are formed. MetHb is reduced by metHb reductase, while ${\text{O}}_2^{•-}$ is converted to H₂O₂ by superoxide dismutase (SOD). In the presence of transition metals such as Fe²⁺ or Cu⁺ a reaction between ${\text{O}}_2^{•-}$ and H₂O₂ occurs yielding hydroxyl radical (OH^•) (Haber Weiss reaction). Catalase, glutathione peroxidases (GPx), and peroxiredoxins (PRXs) decompose H₂O₂. The antioxidant system is completed with non-enzymatic low molecular weight scavengers, such as glutathione, ascorbic acid, and vitamin E. SOD, superoxide dismutase; GPx, glutathione peroxidase; PRXs, peroxiredoxins; GSH, reduced glutathione; GSSG, glutathione disulfide; GSR, glutathione-disulfide reductase; NADP⁺, nicotinamide adenine dinucleotide phosphate; NADPH, reduced NADP; G6PDH, glucose-6-phosphate dehydrogenase; Trx(r), reduced thioredoxin; Trx(ox), oxidized thioredoxin; TrxR, thioredoxin reductase.