Biochimica et Biophysica Acta, 691 (1982) 300-308 Elsevier Biomedical Press Alterations of Red Cell Membrane Proteins and Hemoglobin Under Natural and Experimental Oxidant Stress N. Alloisio, D. Michelon, E. Bannier, A. Revol, Y. Beuzard, and J. Delaunay We compared on red cell membrane proteins and hemoglobin (Hb) the effects of (i) natural oxidant stress that has been suggested to occur in a variety of oxidative hemolytic anemias, and (ii) experimental stress induced by hydrogen peroxide. SDS-polyacrylamide gel electrophoresis was used for protein analysis. Under natural conditions (thalassemias, hemoglobinopathies with Hb unstability), a high molecular weight polymer (HMWP) and variable amounts of globin mono- and dimers became apparent. Furthermore, a major 12 kDa polypeptide, its dimer, and conspicuous spectrin degradation products in the band 2.2-2.6 region occurred in a patient carrying the highly unstable Hb Hammersmith. Under experimental conditions, incubation of erythrocyte ghosts with H2O2 in the presence of minimal concentration (25 uM) of Hb generated a HMWP at the expense of membrane proteins, mainly spectrin. Incubation of a diluted (200 uM) membrane-free hemolysate with H2O2 induced a HMWP, an array of globin oligomers and a 12 kDa polypeptide similar to that mentionned above. Therefore, the damage to the red cell membrane present in various oxidative hemolytic anemias, including polypeptide polymerisation and breakdown, can be produced by experimental oxidant stress. These observations support the view that the alterations described in the patients result directly from oxidative reactions. However, we did not observe in the patient the sharp breakdown of polyunsaturated fatty acids that was triggered in vitro by H2O2 in the presence of Hb acting as a catalyst. In most cases, oligo- and polymers were resistant to B-mercaptoethanol, and the chemical nature of the underlying cross-links is discussed. To our knowledge, the 12 kDa polypeptide, that we consider as arising from globin proteolysis, has never been reported under pathological conditions. Received September 14, 1981. Revised manuscript received March 12, 1982 Key words: Erythrocyte membrane protein; Hemoglobin; Hemolytic anemia; Oxidative stress