Isolation and partial characterization of the human erythrocyte band 7 integral membrane protein

Monoclonal antibodies to the Mr 31,000 major integral membrane protein of the human erythrocyte band 7 region were used to identify the corresponding polypeptide chain and epitope-carrying fragments on immunoblots. Analysis of the erythrocyte membrane, membrane fractions, and cytosol revealed that the Mr 31,000 band 7 integral membrane protein is unique and not related to any of the other water-soluble or membrane-bound band 7 components. Cross-reacting proteins were identified in the membranes of other mammalian erythrocytes and in cell lines of epithelial and lymphoid origin. Proteolytic digestion of intact human erythrocytes or erythrocyte membranes demonstrated that the band 7 integral membrane protein has an intracellular domain larger than Mr 12,000; it does not have an extracellular one. One of the monoclonal antibodies was employed for the isolation of band 7 integral membrane protein by immunoaffinity chromatography; subsequent Edman degradation revealed a blocked N-terminus.