Apell Hans-Jürgen
Department of Biology, University of Konstanz, Fach M635, Germany.
Ann N Y Acad Sci. 2003 Apr;986:133-40. doi: 10.1111/j.1749-6632.2003.tb07150.x.
In the Na,K-ATPase the charge-translocating reaction steps were found to be binding of the third Na(+) ion to the cytoplasmic side and the release of all three Na(+) ions to the extracellular side as well as binding of the two K(+) ions on the extracellular side. The conformation transition E(1) --> E(2) was only of minor electrogenicity; all other reaction steps produced no significant charge movements. In the SR Ca-ATPase and the gastric H,K-ATPase, all ion-binding and -release steps were identified to move charge through the membrane. The high-resolution structure of the SR Ca-ATPase in state E(1) revealed the position of the ion-binding sites in the transmembrane part of the protein. If the same arrangement is assumed for the Na pump, the missing expected charge movements in state E(1) may to be assumed to be apparent effects. With the proposal that binding of 2 Na(+) or 2 K(+) is compensated correspondingly by H(+) ions, agreement between structural and functional aspects is obtained. Investigations of the pH-dependence of ion-binding steps indicate competition between the ions and electrogenic H(+) binding in support of this concept.
在钠钾ATP酶中，发现电荷转运反应步骤包括第三个Na⁺离子与胞质侧结合、所有三个Na⁺离子释放到细胞外侧以及两个K⁺离子在细胞外侧结合。构象转变E(1)→E(2)仅具有较小的电致性；所有其他反应步骤均未产生明显的电荷移动。在肌浆网钙ATP酶和胃H⁺，K⁺-ATP酶中，所有离子结合和释放步骤均被确定为通过膜移动电荷。E(1)状态下肌浆网钙ATP酶的高分辨率结构揭示了该蛋白跨膜部分中离子结合位点的位置。如果假设钠泵具有相同的排列方式，那么E(1)状态下预期缺失的电荷移动可能被认为是表观效应。提出2个Na⁺或2个K⁺的结合由H⁺离子相应补偿，从而在结构和功能方面达成了一致。对离子结合步骤的pH依赖性研究表明离子与电致性H⁺结合之间存在竞争，支持了这一概念。
