The cytoplasmic domain of band 3 serves as a center of erythrocyte membrane organization and constitutes the major substrate of erythrocyte tyrosine kinases. Tyrosine phosphorylation of band 3 is induced by several physiological stimuli including malaria parasite invasion, cell shrinkage, normal cell aging, and oxidant stress (thalassemias, sickle cell disease, G6PDH deficiency, etc). In an effort to characterize the biologic sequelae of band 3 tyrosine phosphorylation, we have looked for changes in the polypeptide’s function that accompany its phosphorylation. We report that tyrosine phosphorylation promotes dissociation of band 3 from the spectrin-actin skeleton as evidenced by: i) a decrease in ankyrin affinity in direct binding studies, ii) an increase in detergent extractability of band 3 from ghosts, iii) a rise in band 3 cross-linkability by BS3, iv) significant changes in erythrocyte morphology, and v) elevation of the rate of band 3 diffusion in intact cells. Because release of band 3 from its ankyrin and adducin linkages to the cytoskeleton can facilitate changes in multiple membrane properties, tyrosine phosphorylation of band 3 is argued to enable adaptive changes in erythrocyte biology that permit the cell to respond to the above stresses.
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