Tanoue Kan, Kaya Shunji, Hayashi Yutaro, Abe Kazuhiro, Imagawa Toshiaki, Taniguchi Kazuya, Sakaguchi Kazuyasu
Biological Chemistry, Division of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810.
J Biochem. 2006 Oct;140(4):599-607. doi: 10.1093/jb/mvj191. Epub 2006 Sep 20.
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.
猪肾钠钾ATP酶制剂在钠-对硝基苯磷酸酶（Na-pNPPase）活性方面对pNPP表现出正协同效应。在pNPP饱和条件下对Na-pNPPase活性、钠ATP酶（Na-ATPase）活性和磷酸化酶（EP）积累的测量显示出几种不同的ATP亲和力。pNPP的存在使EP的最大量和Na-ATPase活性均降低至一半，显示出对于EP形成的ATP亲和力降低了4倍和3700倍，对于Na-ATPase活性的亲和力降低了7倍和1300倍。尽管可用的pNPP位点减少，但磷酸化过程中低浓度ATP的存在使Na-pNPPase活性提高了2倍。然而，较高浓度的ATP抑制了Na-pNPPase活性，而更高浓度的ATP则使磷酸化和Na-ATPase活性均增加至最高水平。无ATP和有ATP时，最大Na-pNPPase活性分别比最大Na-ATPase活性高1.7倍和3.4倍。这些数据以及pNPP对Na-ATPase活性和酶结合ATP量的依赖性降低提供了新的证据，表明ATP、pNPP以及ATP与pNPP分别诱导不同的亚基相互作用，导致四聚体钠钾ATP酶中最大钠依赖性催化活性存在差异。
