Comparative study of the cytoplasmic domain of band 3 from human and rabbit erythrocyte membranes.

The cytoplasmic domain of band 3 (cdb3) is thought to play an important role in human erythrocyte aging. In order to investigate the role of cdb3 during rabbit erythrocyte aging, we compared rabbit cdb3 with the corresponding protein from human erythrocyte membranes. We describe a purification procedure for rabbit cdb3 comparing rabbit and human cdb3 on sodium dodecyl sulphate-polyacrylamide electrophoresis, we found fragments of different molecular weights, implying different chymotryptic cuts in the two species. Anti-human antibodies did not bind to the rabbit cdb3; we also noticed structural differences in the protein between the two species, which may also play a role in the aging processes. Rabbit erythrocyte membranes have a higher capacity of binding hemichromes, due to the higher content of band 3. While in rabbit erythrocyte membranes only one binding site for hemichromes (corresponding to cdb3) was found, we confirmed the existence of two binding sites in human membranes. The second binding site probably corresponds to glycophorin, a protein not present in rabbit membranes.