Hemoglobin-mediated selenium export from red blood cells.

On the basis of the fact that selenium from selenite binds to hemoglobin (Hb), we investigated the missing process in the selenium export from red blood cells (RBCs), i.e., the transfer of selenium bound to Hb to RBC membrane proteins. To elucidate the molecular events of the Hb-associated selenium export from RBC, a Hb-Se complex was synthesized from thiol-exchange of Cys-beta93 in Hb with penicillamine-substituted glutathione selenotrisulfide, as a model of major metabolic intermediates, and then interactions between the Hb-Se complex and RBC inside-out vesicles (IOVs) were examined. Selenium bound to Hb was transferred to the IOV membrane on the basis of the intrinsic interactions between Hb and the cytoplasmic domains of band 3 protein (CDB3). The observed selenium transfer was inhibited by the pretreatments of IOVs with iodoacetamide and the alpha-chymotrypsin digestion, indicating that the Hb mediates the selenium transfer to the thiol groups of CDB3. In addition, it was found that deoxygenated Hb, with a high binding affinity for CDB3, more favorably transferred selenium to the IOV membranes than oxygenated Hb, with a low affinity. When selenium export from RBC to the plasma was examined by continuously introducing nitrogen gas, the selenium export rate was promoted with an increase in the rate of deoxygenated Hb. Overall, these data suggested that Hb could possibly play a role in the selenium export from RBC treated with selenite in an oxygen-linked fashion.