Han C S, Tobin T, Akera T, Brody T M
Biochim Biophys Acta. 1976 May 13;429(3):993-1005. doi: 10.1016/0005-2744(76)90344-2.
The effects of several alkali metal cations on the relationship between steady state phospho-enzyme levels and initial velocity and equilibrium levels of [3H]-ouabain binding to (Na+ + K+)-ATPase (ATP phosphohydrolase EC 3.6.1.3.) were examined. Only Na+ increased both phospho-enzyme and [3H] ouabain binding levels above those observed in the presence of Mg2+ alone. While Na+ stimulated phosphorylation with an apparent Km of about 1 mM, its stimulation of [3H] ouabain binding was biphasic, the lower Km for stimulation corresponding to the Km for formation of phospho-enzyme. Among the other alkali metal cations, potassium, rubidium and lithium were at least eight times more effect in reducing phospho-enzyme levels than in reducing [3H] ouabain binding. This discrepancy is not due to the stability of the enzyme-ouabain complex, nor to any action on the rates of formation or dissociation of the enzyme-ouabain complex. The data thus suggest that [3H] ouabain interacts with the K+, Rb+ or Li+ -enzyme complexes. For Li+, this hypothesis is further supported by the observation that Li+ can cirectly increase the equilibrium level of [3H] ouabain binding to this enzyme under certain conditions.
研究了几种碱金属阳离子对稳态磷酸化酶水平与[3H]哇巴因与（Na+ + K+）-ATP酶（ATP磷酸水解酶，EC 3.6.1.3）结合的初始速度及平衡水平之间关系的影响。只有Na+能使磷酸化酶水平和[3H]哇巴因结合水平高于仅存在Mg2+时所观察到的水平。虽然Na+以约1 mM的表观Km刺激磷酸化作用，但其对[3H]哇巴因结合的刺激是双相的，较低的刺激Km对应于磷酸化酶形成的Km。在其他碱金属阳离子中，钾、铷和锂降低磷酸化酶水平的作用至少比降低[3H]哇巴因结合的作用大八倍。这种差异既不是由于酶-哇巴因复合物的稳定性，也不是由于对酶-哇巴因复合物形成或解离速率的任何作用。因此，数据表明[3H]哇巴因与K+、Rb+或Li+-酶复合物相互作用。对于Li+，这一假设得到了以下观察结果的进一步支持：在某些条件下，Li+可直接增加[3H]哇巴因与该酶结合的平衡水平。
