Inhibition of hemin-induced hemolysis by desferrioxamine: binding of hemin to red cell membranes and the effects of alteration of membrane sulfhydryl groups.

Hemin binds to red cell membranes during hemin-induced hemolysis but the precise mechanism of hemolysis has not been characterized. Desferrioxamine (DFO), an iron chelator, inhibited hemin-induced hemolysis. DFO partially prevented hemin binding to red cell membranes and partially removed previously bound hemin. Glutathione, an intracellular sulfhydryl compound, also inhibited hemin-induced hemolysis but was only about one tenth as potent as DFO. Decrease of membrane sulfhydryl groups by treatment of cells with either N-ethylmaleimide (NEM) or diamide (azodicarboxylic acid bis [dimethylamide]) enhanced hemin-induced hemolysis. Enhancement of hemin-induced hemolysis by NEM and diamide and inhibition of hemolysis by DFO were independent with no evidence of synergism or interference between the two processes. Red cell membranes were saturated with hemin at approximately 75 nmol per mg protein. DFO decreased the hemin saturation level to 25 nmol per mg protein. In the presence of DFO, hemin was bound as the DFO-hemin complex since membranes preferentially removed DFO-hemin complexes from mixtures of complexed and free hemin while free DFO was not bound by the membranes. Access to the inner surface of the membrane was required for binding of the DFO-hemin complex since DFO completely prevented hemin binding in intact cells but not in cells undergoing hemolysis or red cell ghosts. Approximately 50 x 10(6) molecules of hemin were bound to the membrane of one red cell following hemin-induced hemolysis.