Journal Article

Na<sup>+</sup>- and K<sup>+</sup>-Dependent Oligomeric Interconversion among αβ-Protomers, Diprotomers and Higher Oligomers in Solubilized Na<sup>+</sup>/K<sup>+</sup>-ATPase

Takayuki Kobayashi, Yoshikazu Tahara, Hitoshi Takenaka, Kunihiro Mimura and Yutaro Hayashi

in The Journal of Biochemistry

Published on behalf of The Japanese Biochemical Society

Volume 142, issue 2, pages 157-173
Published in print August 2007 | ISSN: 0021-924X
Published online August 2007 | e-ISSN: 1756-2651 | DOI: http://dx.doi.org/10.1093/jb/mvm150
Na+- and K+-Dependent Oligomeric Interconversion among αβ-Protomers, Diprotomers and Higher Oligomers in Solubilized Na+/K+-ATPase

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Protein fractions of a higher-oligomer (H), (αβ)2-diprotomer (D) and αβ-protomer (P) were separated from dog kidney Na+/K+-ATPase solubilized in the presence of NaCl and KCl. Na+/K+-dependent interconversion of the oligomers was analysed using HPLC at 0°C. With increasing KCl concentrations, the content or amount of D increased from 27.6 to 54.3% of total protein, i.e. ΔCmax = 26.7%. ΔCmax for the sum of D and H was equivalent to the absolute value of ΔCmax for P, regardless of the anion present, indicating that K+ induced the conversion of P into D and/or H, and Na+ had the opposite effect. When enzymes that had been denatured to varying degrees by aging were solubilized, ΔCmax increased linearly with the remaining ATPase activity. The magnitude of the interconversion could be explained based on an equilibrium of D ⇌ 2P, assuming 50-fold difference in the Kd between KCl and NaCl, and coexistence of unconvertible oligomers, which comprised as much as 39% of the eluted protein. Oligomeric interconversion, determined as a function of the KCl or NaCl concentration, showed K0.5s of 64.8 μM and 6.50 mM for KCl and NaCl, respectively, implying that oligomeric interconversion was coupled with Na+/K+-binding to their active transport sites.

Keywords: dog kidney; oligomeric interconversion; oligomeric structure; Na+/K+-ATPase; solubilized membrane protein

Journal Article.  13566 words.  Illustrated.

Subjects: Biochemistry

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