The isolated cytoplasmic domain of band 3 binds calcium at physiological salt concentration and neutral PH.
Calcium is known to be a potent but partial intracellular inhibitor of band 3 anion exchange. Here we test the hypothesis that the cytoplasmic domain of band 3 (CDB3) contains a calcium binding site. Calcium binding to CDB3 was monitored by measuring the formation of the Aresenazo III-calcium complex at various constant CDB3 concentrations. These experiments were performed at physiological salt and neutral pH. The calcium-CDB3 dissociation constant was estimated to be less than or equal to 24 microM. We also found that the Arsenazo III-calcium complex binds to CDB3, while the free dye does not bind. We conclude that CDB3 contains a site which is capable of binding free calcium under physiological conditions. A specific role for this site in inhibition of band 3 anion exchange is suggested, but that role remains to be established.
Salhany
J M
JM
Department of Veterans Affairs Medical Center, Omaha, Nebraska.
Cordes
K A
KA
D000595:Amino Acid Sequence; D001457:Anion Exchange Protein 1, Erythrocyte / Q000378:metabolism*; D002118:Calcium / Q000097:blood*; D003593:Cytoplasm / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008962:Models, Theoretical; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D011485:Protein Binding; D013053:Spectrophotometry
D001457:Anion Exchange Protein 1, Erythrocyte; D002118:Calcium