Hemoglobin-mediated selenium export from red blood cells.
ABSTRACT
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-ƒÀ93 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 ƒ¿-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.