Heme degradation in the presence of glutathione: A proposed mechanism to account for the high levels of non-heme iron found in the membranes of hemoglobinopathic red blood cells

Unstable hemoglobins and oxidative conditions tend to produce hemichromes which demonstrably release their heme to the erythrocyte membrane, with consequent lipid peroxi dation and cell lysis. High levels of non-heme iron are also found in such circumstances, but the origin of this iron is uncertain. In the present work, we show that reduced glutathione (GSH) is able to degrade heme in solution with a pH optimum of 7. Degradation depended on the presence of oxygen and on heme and GSH concentrations. It was inhibited by catalase and superoxide dismutase, implicating the involvement of perferryl reactive species in the process of heme degradation. Heme degradation at pH 7 and 37°C is rapid (t_1/2 = 70 s) and results in the release of iron from heme. Heme that was dissolved in red blood cell ghosts is also degraded by GSH with a concomitant increase in non-heme iron, most of which (75%) remains associated with the cell membrane. Loading of intact erythrocytes with heme was followed by time-dependent decrease of membrane-associated heme and caused an acceleration of the hexose monophosphate shunt due to the production of H₂O₂ and the oxidation of intracellular GSH. Most of the activation of the hexose monophosphate pathway was due to redox cycling of iron, since iron chelators inhibited it considerably. These results explain the origin of non-heme iron found in the membrane of sickle cells and the oxidative stress that is observed in these and other abnormal erythrocytes.