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Journal of Biochemistry Advance Access published online on September 20, 2006
Journal of Biochemistry, doi:10.1093/jb/mvj191
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© 2006 The Japanese Biochemical Society.
Received September 4, 2006
Accepted September 12, 2006

Regular Paper

New Evidence for ATP Binding Induced Catalytic Subunit Interactions in Pig Kidney Na/K-ATPase

Kan Tanoue 1, Shunji Kaya 1, Yutaro Hayashi 2, Kazuhiro Abe 1, Toshiaki Imagawa 1, Kazuya Taniguchi 1 *, and Kazuyasu Sakaguchi 1

1 Biological Chemistry, Division of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan
2 Department of Biochemistry, Kyorin University School of Medicine, Mitaka, Tokyo 181-8611, Japan

* To whom correspondence should be addressed.
Kazuya Taniguchi, E-mail: ktan40{at}mvd.biglobe.ne.jp


  Abstract

Pig kidney Na/K-ATPase preparations showed a positive cooperative effect for pNPP in Na-pNPPase activity. Measurements of the Na-pNPPase activity, Na-ATPase activity and the accumulation of phosphoenzyme (EP) under conditions of pNPP saturation showed several different ATP affinities. The presence of pNPP reduced both the maximum amount of EP and Na-ATPase activity to half showing a value of 4 and a 3700-fold reduced ATP affinity for EP formation, and a 7 and 1300-fold reduced affinity for Na-ATPase activity. The presence of low concentrations of ATP in the phosphorylation induced a 2-fold enhancement in Na-pNPPase activity despite a reduction in available pNPP sites. However, higher concentrations of ATP inhibited the Na-pNPPase activity and a much higher concentration of ATP increased both the phosphorylation and Na-ATPase activity to the maximum levels. The maximum Na-pNPPase activity was 1.7 and 3.4-fold higher without and with ATP, respectively, than the maximum Na-ATPase activity. These data and the pNPP dependent reduction in both Na-ATPase activity and the amount of enzyme bound ATP provide new evidence to show that ATP, pNPP and ATP with pNPP, respectively, induce different subunit interactions resulting a difference in the maximum Na+-dependent catalytic activity in tetraprotomeric Na/K-ATPase.

Keywords: Na/K-ATPase; P-type ATPase; Oligomer; Subunit interactions; Membrane bound enzyme.
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