title: The binding of Ca2+ to solubilized band 3 protein of the human erythrocyte membrane.
abstract: The binding of 45Ca2+ to isolated band 3 protein, the anion transport protein of the human erythrocyte membrane, was studied by equilibrium dialysis. The protein was solubilized and purified by either the nonionic detergent Ammonyx-L0 or acetic acid. Each preparation of band 3 protein showed a single high-affinity Ca2+ binding site and several Ca2+ binding sites of lower affinity. The association constant of the high-affinity site was 4-13 X 10(4)M-1; it was only moderately dependent on ionic strength. Mg2+ effectively competed with Ca2+ for the site. Anion exchange across the human erythrocyte membrane is inhibited by micromolar concentrations of intracellular Ca2+. Our results suggest that this inhibition is due to the binding of the cation to a single site on band 3 protein.
mesh_terms: D001457:Anion Exchange Protein 1, Erythrocyte / Q000378:metabolism*; D001667:Binding, Competitive; D002118:Calcium / Q000097:blood*; D006801:Humans; D007700:Kinetics; D008274:Magnesium / Q000097:blood; D011485:Protein Binding; D014461:Ultracentrifugation
chemical_list: D001457:Anion Exchange Protein 1, Erythrocyte; D008274:Magnesium; D002118:Calcium