FORMATION OF SUPEROXIDE IN AUTOXIDATION OF ISOLATED ALPHA AND BETA CHAINS OF HUMAN HEMOGLOBIN AND ITS INVOLVEMENT IN HEMICHROME PRECIPITATION

The purpose of the work reported here is to look at O−2 production during autoxidation of the isolated α and β chains of human hemoglobin. The formation of superoxide by isolated chains. in fact, may be involved in pathological phenomena observed in red blood cell diseases where excess of either α or β chains is produced because of inherited defects of synthesis (thalassemus). The autoxidation of the oxygenated chains of human hemoglobin is followed by the transformation of the oxidized molecule (high-spin Fe3+) into a species absorbing as a low-spin Fe3+ compound, that is a hemichrome, which tends to precipitate. The overall process may be described by the following reactions: Depending on conditions the different steps proceed with different relative rates and therefore may overlap to a greater or lesser extent. The results obtained indicate that superoxide is produced during autoxidation of the isolated α and β chains of human hemoglobin. This conclusion has been reached on the basis of an experimental approach based on cooxidation of epinephrine to adrenochrome during O−2 production and inhibition of this effects by superoxide dismutase. In addition the rate of precipitation is, in all cases, very much reduced upon addition of either superoxide dismutase or catalase. These facts seem to imply very strongly that oxygen radicals are involved also in the precipitation following oxidation and hemichrome formation in the chains. In particular the effect of superoxide dismutase implies the involvement of O−2. Thus production of O−2 could well be one of the important events leading to alteration of the red cell membrane and consequently to reduced life span of thalassemic erythrocytes.