[Hemoglobin--source of reactive oxygen species]

Erythrocytes are especially vulnerable to reactive oxygen species because of their direct role in oxygen transport. Moreover, hemoglobin contains iron ions (Fe²⁺), which catalyze both the Fenton reaction and lipid peroxidation. Reactive oxygen species in erythrocytes are also generated through nonenzymatic and enzymatic processes of heme degradation. The nonenzymatic process of heme degradation is initiated by e.g. hydrogen peroxide, whereas the process of enzymatic degradation is under the influence of heme oxygenase. In both cases biliverdin, carbon monoxide (CO) and iron ions (Fe²⁺) are generated. These products of heme degradation can initialize the oxidative processes within erythrocytes, but at low concentrations exhibit cytoprotective properties.