title: Fine structure of the band 3 protein in human red cell membranes: freeze-fracture studies.
abstract: The major red cell membrane protein, band 3, is a glycoprotein which extends across the membrane from the extracellular space into the cytoplasmic compartment. It is widely held that band 3 is a component of the intramembrane particles (IMP) which can be demonstrated by freeze-fracture electron microscopy. In this study, we find that the outer surface poles of the IMP can be seen by freeze-etching after they are unmasked by proteolysis under conditions which excise the surrounding sialopeptides from the membrane. The poles appear as distinctive projections, 30--50 A in diameter, the "ES particles." The ES particles remain associated with the outer surface of the membrane following cleavage of the band 3 polypeptide by chymotrypsin or pronase. This is consistent with previous biochemical studies which have shown that the 38,000-dalton outer surface segment of band 3 is intercalated in the lipid bilayer. A granulofibrillar component at the inner surface of the membrane is provisionally identified as the 40,000-dalton inner-surface domain of band 3.
mesh_terms: D004910:Erythrocyte Membrane / Q000648:ultrastructure*; D004912:Erythrocytes / Q000648:ultrastructure*; D005614:Freeze Fracturing; D006023:Glycoproteins / Q000097:blood*; D006801:Humans; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000097:blood*; D010447:Peptide Hydrolases / Q000378:metabolism; D011487:Protein Conformation
chemical_list: D006023:Glycoproteins; D046911:Macromolecular Substances; D008565:Membrane Proteins; D010447:Peptide Hydrolases