Sullivan C W, Volcani B E
Proc Natl Acad Sci U S A. 1974 Nov;71(11):4376-80. doi: 10.1073/pnas.71.11.4376.
An ATP-hydrolyzing activity with the properties of a Mg(2+)-dependent (Na(+),K(+))-ATPase (ATP phosphohydrolase, EC 3.6.1.3) from a 20-fold purified plasma membrane fraction of the marine diatom, Nitzschia alba is described. The basal activity requires Mg(2+) and further stimulation by Na(+) or Na(+) plus K(+) is dependent on the presence of Mg(2+); Mn(2+) or Co(2+) can partially substitute for the divalent cation requirement but Ca(2+) equimolar with Mg(2+) inhibits the activity by 54%. ATP is the preferred substrate for the Na(+) plus K(+) stimulated activity, while CTP, UTP, and ADP are only slightly hydrolyzed. The apparent K(m) is 8 x 10(-4) M ATP. The ATP hydrolysis-rate is dependent on the relative concentrations of Na(+) and K(+); the K(0.5) for Na(+) and K(+) are 2 mM and 50 mM, respectively. Basal activity is synergistically stimulated by Na(+) plus K(+) only at certain ion concentrations and shows a strong specificity for both cations. In the presence of Na(+) at 5 mM and K(+) at 350 mM, the ATPase is completely inhibited by p-chloromercuric benzoic acid 10(-4) M, N-ethyl maleimide 10(-3) M, and iodoacetamide 10(-2) M, but is insensitive to ouabain at 10(-7) to 10(-3) M. This study demonstrates for the first time that algal plasma membrane contains an ATPase that is synergistically stimulated by Na(+) and K(+).
本文描述了从海洋硅藻——白色菱形藻（Nitzschia alba）经20倍纯化的质膜组分中提取的一种具有Mg(2+)依赖性（Na(+)，K(+)）-ATP酶（ATP磷酸水解酶，EC 3.6.1.3）特性的ATP水解活性。基础活性需要Mg(2+)，Na(+)或Na(+)加K(+)的进一步刺激依赖于Mg(2+)的存在；Mn(2+)或Co(2+)可部分替代二价阳离子需求，但与Mg(2+)等摩尔的Ca(2+)会使活性抑制54%。ATP是Na(+)加K(+)刺激活性的首选底物，而CTP、UTP和ADP仅被轻微水解。表观K(m)为8×10(-4) M ATP。ATP水解速率取决于Na(+)和K(+)的相对浓度；Na(+)和K(+)的K(0.5)分别为2 mM和50 mM。基础活性仅在特定离子浓度下受到Na(+)加K(+)的协同刺激，并且对两种阳离子都表现出很强的特异性。在5 mM Na(+)和350 mM K(+)存在下，该ATP酶被10(-4) M对氯汞苯甲酸、10(-3) M N-乙基马来酰亚胺和10(-2) M碘乙酰胺完全抑制，但对10(-7)至10(-3) M的哇巴因不敏感。这项研究首次证明藻类质膜含有一种受Na(+)和K(+)协同刺激的ATP酶。
