title: New evidence for ATP binding induced catalytic subunit interactions in pig kidney Na/K-ATPase.
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 3,700-fold reduced ATP affinity for EP formation, and a 7 and 1,300-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.
authors.affiliation: Biological Chemistry, Division of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810. ktan40@mvd.biglobe.ne.jp
authors.forename: Kan
authors.initials: K
authors.lastname: Tanoue
authors.forename: Shunji
authors.initials: S
authors.lastname: Kaya
authors.forename: Yutaro
authors.initials: Y
authors.lastname: Hayashi
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Abe
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Imagawa
authors.forename: Kazuya
authors.initials: K
authors.lastname: Taniguchi
authors.forename: Kazuyasu
authors.initials: K
authors.lastname: Sakaguchi
mesh_terms: D009597:4-Nitrophenylphosphatase / Q000737:chemistry*; D000255:Adenosine Triphosphate / Q000737:chemistry*; D000818:Animals; D020134:Catalytic Domain; D004789:Enzyme Activation; D007668:Kidney / Q000201:enzymology; D008954:Models, Biological; D009596:Nitrophenols / Q000737:chemistry; D009943:Organophosphorus Compounds / Q000737:chemistry; D010766:Phosphorylation; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry*; D013552:Swine
chemical_list: D009596:Nitrophenols; D009943:Organophosphorus Compounds; C008644:nitrophenylphosphate; D000255:Adenosine Triphosphate; D009597:4-Nitrophenylphosphatase; D000254:Sodium-Potassium-Exchanging ATPase