Reassociation of ankyrin with band 3 in erythrocyte membranes and in lipid vesicles.

The binding of human erythrocyte ankyrin (band 2.1) to the erythrocyte membrane has been characterized by reassociating purified ankyrin with ankyrin-depleted inside-out vesicles. Ankyrin reassociates at high affinity with a limited number of protease-sensitive sites located only on the cytoplasmic side of the erythrocyte membrane. Depleting the vesicles of band 4.2 does not affect their binding capacity. A 45,000-dalton polypeptide derived from the cytoplasmic portion of band 3 competitively inhibits the binding of ankyrin to inside-out vesicles. Although the bulk of band 3 molecules appear to have the potential for binding ankyrin, nly a fraction of the band 3 molecules in native membranes or in reconstituted liposomes actually provides accessible high affinity ankyrin binding sites.