title: The carboxyl-terminal domain of human erythrocyte band 3. Description, isolation, and location in the bilayer.
abstract: Band 3, the anion channel protein of the human erythrocyte, is the major transmembrane glycoprotein of the erythrocyte membrane. The protein is distributed in a broad 88,000-98,000-dalton band on gel electrophoresis. Previous investigations have defined an NH2-terminal cytoplasmic domain and an adjacent membrane-spanning domain of the Band 3 molecule. The fragments containing these domains appear as discrete bands by sodium dodecyl sulfate polyacrylamide gel electrophoresis. A carboxyl-terminal fragment of the Band 3 molecule was generated by digestion with chymotrypsin at the external face of intact erythrocytes. This fragment appears as a broad band of Mr = 34,000-45,000. It has a site accessible to lactoperoxidase at the internal face of the membrane and must, therefore, span the membrane. Slices from different regions of the broad electrophoretic band of the carboxyl-terminal fragment of Band 3 all have identical peptide maps. The same is true of Band 3. Therefore, despite their heterogeneous appearance on gels, Band 3 and its proteolytic fragments are homogeneous polypeptides. This conclusion is supported by the finding of an unique NH2-terminal tetrapeptide sequence for one Band 3 fragment. The apparent heterogeneity of Band 3 and its carboxyl-terminal region may reflect variability of glycosylation or sodium dodecyl sulfate binding.
mesh_terms: D000345:Affinity Labels; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D001457:Anion Exchange Protein 1, Erythrocyte; D001798:Blood Proteins / Q000032:analysis*; D002918:Chymotrypsin; D004910:Erythrocyte Membrane / Q000032:analysis*; D004912:Erythrocytes / Q000032:analysis*; D006801:Humans; D008051:Lipid Bilayers / Q000032:analysis; D008565:Membrane Proteins / Q000032:analysis*; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis*; D013654:Taurine / Q000031:analogs & derivatives; D014357:Trypsin
chemical_list: D000345:Affinity Labels; D000596:Amino Acids; D001457:Anion Exchange Protein 1, Erythrocyte; D001798:Blood Proteins; D008051:Lipid Bilayers; D008565:Membrane Proteins; D010446:Peptide Fragments; D013654:Taurine; C010861:NAP taurine; D002918:Chymotrypsin; D014357:Trypsin