title: Conformational changes in the alpha-subunit and cation transport by pure Na, K-ATPase.
abstract: In this study we examined the coupling of transitions between phosphoforms, E1P and E2P, of pure Na, K-ATPase to cation translocation after selective proteolysis of the alpha-subunit. Cleavage with trypsin at the carboxyl terminal side (Bond 1) of the aspartyl phosphate residue or with chymotrypsin at the aminoterminal side (Bond 1) blocks Na, K-ATPase and Na, K-transport, but the two splits have widely different effects on partial reactions. Cleavage of bond 3 blocks transition from E1P to E2P and abolish both (ADP + ATP)-Na/Na exchange and (ATP + Pi)-Rb/Rb exchange reactions in vesicles reconstituted with pure Na, K-ATPase. Cleavage of bond 1 interferes neither with the transitions nor with the exchange reactions. The results agree with the notion that the transitions between the phosphoforms, E1P and E2P, of the alpha-subunit are coupled to flipping of cation sites between inside exposed (E1) and an outside exposed states (E2).
mesh_terms: D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D001693:Biological Transport, Active; D002918:Chymotrypsin; D007700:Kinetics; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D008970:Molecular Weight; D010446:Peptide Fragments / Q000032:analysis; D010766:Phosphorylation; D011188:Potassium / Q000378:metabolism*; D011487:Protein Conformation; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D014357:Trypsin
chemical_list: D008051:Lipid Bilayers; D046911:Macromolecular Substances; D010446:Peptide Fragments; C032197:beta-aspartyl phosphate; D001224:Aspartic Acid; D012964:Sodium; D002918:Chymotrypsin; D014357:Trypsin; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D011188:Potassium