Abstract
4-Dimethylaminophenol (DMAP) forms ferrihemoglobin by catalytic transfer of electrons from ferrohemoglobin to oxygen. In solutions of purified human hemoglobin, quick binding of oxidized DMAP to the globin moiety of hemoglobin terminates this reaction. Reduced glutathione in high concentrations, as in the red cell, substantially diminished binding of oxidized DMAP to hemoglobin by formation of S,S,S-(2-dimethylamino-5-hydroxy-1,3,4-phenylene)-tris-glutathione (tris(GS)-DMAP), which does not form ferrihemoglobin. In the presence of reduced glutathione, DMAP disappeared more rapidly from hemoglobin solutions than in its absence. The formation of tris(GS)-DMAP in red cells was found to be of importance for the termination of catalytic ferrihemoglobin formation by DMAP in vivo. With low concentrations of GSH, DMAP in hemoglobin solutions formed another conjugate, bis(GS)-DMAP, S,S-(2-dimethylamino-5-hydroxy-1,3-phenylene)-bis-glutathione. Similar to DMAP, bis(GS)-DMAP catalyzed the formation of ferrihemoglobin. As the oxidized bis(GS)-DMAP was bound to hemoglobin more slowly and to a lesser extent, it produced more ferrihemoglobin than DMAP. In contrast to the reactions of DMAP with hemoglobin, hydrogen peroxide and superoxide radicals are involved in the ferrihemoglobin formation by bis(GS)-DMAP. The radicals accelerate the oxidation of bis(GS)-DMAP and thereby the ferrihemoglobin formation.
Published Version
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