Accumulation and drainage of hemin in the red cell membrane

The subject of hemin intercalation in red cell membranes and the correlation of the accumulated hemin level with the membrane pathology was studied. Methods which made use of dioxan and octan-2-ol mixtures to quantitate small amounts of hemin in membranes were developed. Applying these methods, hemin levels were measured in the cytoskeleton and the remaining lipid core of various red cell membranes. The amount of hemin, in both membrane fractions, was higher in pathological cells of sickle cell anemia and beta-thalassemia as compared to normal circulating cells. Correlation exists between the amount of the membrane-accumulated hemin and the severity of the disease. The level of hemin in the membrane was found to be age dependent, old cells in circulation accumulating more hemin than young cells. The level of hemin in all cells tested was much lower than the amount found previously to cause immediate hemolysis when applied externally (Kirschner-Zilber, I., Rabizadeh, E. and Shaklai, N. (1982) Biochim. Biophys. Acta 690, 20-30). This was explained by the differences between the process leading to immediate lysis and membrane changes recognized as pathological by the in-vivo sequestration mechanism. In search of a physiological mechanism which may drain the cell membrane from the hazardeous hemin, albumin, the main serum protein, was found capable of serving as an efficient agent for extracting hemin trapped in red cell membranes. It is suggested that under normal conditions albumin extracts enough hemin to leave the erythrocyte with unharmful hemin amounts, however, under pathological conditions greater amounts accumulate leading to a shorter cell life span.