Abstract
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 Arsenazo 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 ≤ 24 μM. 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.
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