A thiol-mediated active membrane transport of selenium by erythroid anionexchanger
1 protein
ABSTRACT
In this paper, we describe a thiol-mediated and energy-dependent membrane
transport of selenium by erythroid anion exchanger 1 (AE1, also known as
band 3 protein). The AE1 is the most abundant integral protein of red cell
membranes and plays a critical role in the carbon dioxide transport system
in which carbon dioxide is carried as bicarbonate in the plasma. This protein
mediates the membrane transport of selenium, an essential antioxidant micronutrient,
from red cells to the plasma in a manner that is distinct from the already
known anion exchange mechanism. In this pathway, selenium bound to the
cysteine 93 of the hemoglobin ƒÀ chain (Hb-CysƒÀ93) is transported by the
relay mechanism to the Cys317 of the amino-terminal cytoplasmic domain
of the AE1 on the basis of the intrinsic interaction between the two proteins
and is subsequently exported to the plasma via the Cys843 of the membrane-spanning
domain. The selenium export did not occur in plain isotonic buffer solutions
and required thiols, such as albumin, in the outer medium. Such a membrane
transport mechanism would also participate in the export pathways of the
nitric oxide vasodilator activity and other thiol-reactive substances bound
to the Hb-CysƒÀ93 from red cells to the plasma and/or peripherals.