Rodríguez-Navarro Alonso, Benito Begoña
Centro de Biotecnología y Genómica de Plantas, Universidad Politécnica de Madrid, Campus Montegancedo, carretera M-40, km 37.7, 28223-Pozuelo de Alarcón, Madrid, Spain.
Biochim Biophys Acta. 2010 Oct;1798(10):1841-53. doi: 10.1016/j.bbamem.2010.07.009. Epub 2010 Jul 19.
The K(+) and Na(+) concentrations in living cells are strictly regulated at almost constant concentrations, high for K(+) and low for Na(+). Because these concentrations correspond to influx-efflux steady states, K(+) and Na(+) effluxes and the transporters involved play a central role in the physiology of cells, especially in environments with high Na(+) concentrations where a high Na(+) influx may be the rule. In eukaryotic cells two P-type ATPases are crucial in these homeostatic processes, the Na,K-ATPase of animal cells and the H(+)-ATPase of fungi and plants. In fungi, a third P-type ATPase, the ENA ATPase, was discovered nineteen years ago. Although for many years it was considered to be exclusively a fungal enzyme, it is now known to be present in bryophytes and protozoa. Structurally, the ENA (from exitus natru: exit of sodium) ATPase is very similar to the sarco/endoplasmic reticulum Ca(2+) (SERCA) ATPase, and it probably exchanges Na(+) (or K(+)) for H(+). The same exchange is mediated by Na(+) (or K(+))/H(+) antiporters. However, in eukaryotic cells these antiporters are electroneutral and their function depends on a DeltapH across the plasma membrane. Therefore, the current notion is that the ENA ATPase is necessary at high external pH values, where the antiporters cannot mediate uphill Na(+) efflux. This occurs in some fungal environments and at some points of protozoa parasitic cycles, which makes the ENA ATPase a possible target for controlling fungal and protozoan parasites. Another technological application of the ENA ATPase is the improvement of salt tolerance in flowering plants.
活细胞中的钾离子（K⁺）和钠离子（Na⁺）浓度受到严格调控，几乎保持恒定，钾离子浓度高而钠离子浓度低。由于这些浓度对应着流入 - 流出稳态，钾离子和钠离子的流出以及相关转运蛋白在细胞生理学中起着核心作用，特别是在高钠离子浓度的环境中，高钠离子流入可能是常态。在真核细胞中，两种P型ATP酶在这些稳态过程中至关重要，即动物细胞中的钠钾ATP酶以及真菌和植物中的氢离子ATP酶。在真菌中，19年前发现了第三种P型ATP酶，即ENA ATP酶。尽管多年来它一直被认为是真菌特有的酶，但现在已知它存在于苔藓植物和原生动物中。从结构上看，ENA（源自拉丁语exitus natru：钠的排出）ATP酶与肌浆网/内质网钙（Ca²⁺）（SERCA）ATP酶非常相似，它可能将钠离子（或钾离子）与氢离子进行交换。相同的交换由钠离子（或钾离子）/氢离子反向转运蛋白介导。然而，在真核细胞中，这些反向转运蛋白是电中性的，其功能取决于跨质膜的ΔpH。因此，目前的观点是，在外部pH值较高时，ENA ATP酶是必需的，此时反向转运蛋白无法介导钠离子的上坡流出。这种情况发生在一些真菌环境和原生动物寄生周期的某些阶段，这使得ENA ATP酶成为控制真菌和原生动物寄生虫的一个可能靶点。ENA ATP酶的另一个技术应用是提高开花植物的耐盐性。
