在存在寡霉素或ATP的情况下，NaCl对Na⁺/K⁺-ATP酶的对硝基苯磷酸酶活性的刺激作用。
Stimulation of p-nitrophenylphosphatase activity of Na+/K+-ATPase by NaCl with oligomycin or ATP.
作者信息
Homareda Haruo, Ushimaru Makoto
机构信息
Department of Biochemistry, Kyorin University School of Medicine, Mitaka, Tokyo, Japan.
出版信息
FEBS J. 2005 Feb;272(3):673-84. doi: 10.1111/j.1742-4658.2004.04496.x.
It is known that the addition of NaCl with oligomycin or ATP stimulates ouabain-sensitive and K+-dependent p-nitrophenylphosphatase (pNPPase) activity of Na+/K+-ATPase. We investigated the mechanism of the stimulation. The combination of oligomycin and NaCl increased the affinity of pNPPase activity for K+. When the ratio of Na+ to Rb+ was 10 in the presence of oligomycin, Rb+-binding and pNPPase activity reached a maximal level and Na+ was occluded. Phosphorylation of Na+/K+-ATPase by p-nitrophenylphosphate (pNPP) was not affected by oligomycin. Because oligomycin stabilizes the Na+-occluded E1 state of Na+/K+-ATPase, it seemed that the Na+-occluded E1 state increased the affinity of the phosphoenzyme formed from pNPP for K+. On the other hand, the combination of ATP and NaCl also increased the affinity of pNPPase for K+ and activated ATPase activity. Both activities were affected by the ligand conditions. Oligomycin noncompetitively affected the activation of pNPPase by NaCl and ATP. Nonhydrolyzable ATP analogues could not substitute for ATP. As NaE1P, which is the high-energy phosphoenzyme formed from ATP with Na+, is also the Na+-occluded E1 state, it is suggested that the Na+-occluded E1 state increases the affinity of the phosphoenzyme from pNPP for K+ through the interaction between alpha subunits. Therefore, membrane-bound Na+/K+-ATPase would function as at least an (alphabeta)2-diprotomer with interacting alpha subunits at the phosphorylation step.
已知在寡霉素或ATP存在的情况下添加NaCl可刺激Na⁺/K⁺-ATP酶的哇巴因敏感性和K⁺依赖性对硝基苯磷酸酶（pNPPase）活性。我们研究了这种刺激的机制。寡霉素与NaCl的组合增加了pNPPase活性对K⁺的亲和力。当在寡霉素存在下Na⁺与Rb⁺的比例为10时，Rb⁺结合和pNPPase活性达到最大水平且Na⁺被封闭。对硝基苯磷酸（pNPP）对Na⁺/K⁺-ATP酶的磷酸化不受寡霉素影响。因为寡霉素稳定了Na⁺/K⁺-ATP酶的Na⁺封闭E1状态，似乎Na⁺封闭E1状态增加了由pNPP形成的磷酸酶对K⁺的亲和力。另一方面，ATP与NaCl的组合也增加了pNPPase对K⁺的亲和力并激活了ATP酶活性。两种活性都受配体条件影响。寡霉素非竞争性地影响NaCl和ATP对pNPPase的激活。不可水解的ATP类似物不能替代ATP。由于由ATP与Na⁺形成的高能磷酸酶NaE1P也是Na⁺封闭E1状态，因此表明Na⁺封闭E1状态通过α亚基之间的相互作用增加了pNPP形成的磷酸酶对K⁺的亲和力。因此，膜结合的Na⁺/K⁺-ATP酶在磷酸化步骤中至少会作为具有相互作用α亚基的（αβ）₂二聚体发挥作用。
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