TY - JOUR T1 - Ouabain-Induced Changes in the Tertiary And the Quaternary Conformations of (Na<sup>+</sup> + K<sup>+</sup>)-Activated Adenosine Triphosphatase JF - Molecular Pharmacology JO - Mol Pharmacol SP - 53 LP - 56 VL - 18 IS - 1 AU - WU-HSIUNG HUANG AU - AMIR ASKARI Y1 - 1980/07/01 UR - http://molpharm.aspetjournals.org/content/18/1/53.abstract N2 - Purified preparations of (Na+ + Ki+)-activated adenosine triphosphatase (EC 3.6.1.3) contain two major polypeptides: the catalytic subunit (α-subunit), and a glycoprotein (β-subunit) of unknown function. Effects of ouabain on the chemical crosslinking of the subunits in the presence of o-phenanthroline and Cu2+ were studied, and the following results were obtained: (1) When the native enzyme was exposed to 0.25 mM Cu2+ and 1.25 mM o-phenanthroline, a crosslinked α,α-dimer was obtained in the presence of Na+ + ATP, but not in the presence of either Na+, or K+, or K+ + ATP. Exposure of the preformed ouabain-enzyme complex to the same reagent resulted in the formation of the α, α-dimer. The level of this dimer was lower than that obtained from the native enzyme in the presence of Na+ + ATP, and was not affected by Na+, ATP, and K+. (2) When the native enzyme was preincubated with Na+ + Mg2+ + ATP and then exposed to 0.25 mM Cu2+ and 1.25 mM o-phenanthroline, the α,α-dimer was obtained. Addition of K+ to the preincubated enzyme prior to the addition of the crosslinking reagent prevented dimer formation. Addition of ouabain to the preincubated enzyme, did not affect dimer formation but did block the K+ effect on dimer formation. (3) When the native enzyme was exposed to 0.25 mM Cu2+ and 0.5 mM o-phenanthroline, an α,α-dimer was obtained under all ligand conditions except when K+ + ATP was present. With the preformed ouabain-enzyme complex, the dimer was obtained, and its formation was not affected by K+ + ATP. (4) The formation of an α,β-dimer in the presence of Cu2+ and o-phenanthroline was not affected by ouabain. These findings indicate that the minimum quaternary structure of α2β2 existS in both the native enzyme and the ouabain-enzyme complex, but that ouabain binding induces changes in α-subunit conformation and in α-subunit interactions within the oligomeric structure of the enzyme. ER -