ABSTRACT
This chapter discusses formation of methemoglobin (MetHb) and free radicals in erythrocytes. Liganding of dioxygen to hemoglobin is associated with the dislocation of an electron from the iron atom orbital to the molecular orbital of oxygen. The small percentage of MetHb formation that is always present in healthy individuals may be due to destabilization of the oxo-iron bond as a result of the changed electron delocalization. Phenolic compounds are also able to undergo one-electron oxidation in the presence of oxyhemoglobin, thereby forming transient phenoxyl radicals. In the presence of reactive oxygen species such as superoxide or hydrogen peroxide, iron ions play a significant role as prooxidant catalysts. Thiol groups, which are particularly sensitive to oxidative stress, indicate the formation of prooxidants at an early stage before other compounds are affected. Significant decrease of thiol levels even with those xenobiotics having a low MetHb formation rate indicated the formation of oxidizing reaction intermediates in red blood cells.
