Evidence that spectrin binds to macromolecular complexes on the inner surface of the red cell membrane

Spectrin binds to a population of high-affinity sites on the exposed surface of inverted vesicles prepared from human red blood cell ghost membranes. Optimal spectrin binding requires the presence of monovalent salts but does not require calcium or magnesium. The band 2 subunit of spectrin, prepared in SDS, can also bind to vesicles, but isolated band 1 is inactive. Pre-incubation of inverted vesicles with antibodies directed against the cytoplasmic segment of band 3 or against bands 4.1-4.2 inhibits the binding of spectrin to the same vesicles. Antibodies against the cytoplasmic portion of glycophorin A have no effect. These results suggest that spectrin binds to a protein acceptor on the cytoplasmic surface of the red cell membrane which is close to the cytoplasmic segments of bands 3 and 4.1 and/or 4.2.