哇巴因敏感的ATP：ADP交换的胞外钠依赖性，该交换由人红细胞血影中细胞内笼形ATP的光解引发。

External Na dependence of ouabain-sensitive ATP:ADP exchange initiated by photolysis of intracellular caged-ATP in human red cell ghosts.

作者信息

Kaplan J H, Hollis R J

出版信息

Nature. 1980 Dec 11;288(5791):587-9. doi: 10.1038/288587a0.

Abstract

Coupled active transport of Na+ and K+ across cellular plasma membranes is mediated by (Na+ + K+)-stimulated Mg2+-dependent ATPase. Active cation transport by this Na pump involves a cyclic Na-dependent phosphorylation of the enzyme by intracellular ATP and hydrolytic dephosphorylation of the phosphoenzyme, stimulated by K+ (ref. 1). In human red blood cells, skeletal muscle and squid axons, replacement of extracellular K by Na results in a ouabain-sensitive efflux of Na coupled to an influx of extracellular Na. There is apparently no net Na movement nor net hydrolysis of ATP. The rate of Na:Na exchange is stimulated by increased levels of ADP and exchange transport is not observed in cells totally depleted of intracellular ATP. These characteristics suggest that the biochemical mechanism underlying the Na exchange mode of the Na pump involves phosphorylation of the enzyme by ATP (which requires intracellular Na) followed by its dephosphorylation by ADP. Such a reaction has been observed in partially purified (Na+ + K+) ATPase from a variety of sources and its dependence on Na concentration has been described (although not previously for the red cell enzyme). In the present work, intracellular ATP:ADP exchange reaction was initiated by photoreleased ATP following brief irradiation at 350 nm of ghosts containing caged-ATP. The ouabain-sensitive component of the ensuing ATP:ADP exchange reaction shows a biphasic response to extracellular Na. External Na in the range 0--10 mM has an inhibitory effect whilst increasing concentrations beyond this range stimulate the rate of exchange in a roughly linear fashion up to 100 mM Na. These results represent the first direct demonstration of the sidedness of the effects of Na on this partial sequence in the overall enzyme cycle and bear a qualitative resemblance to the Na effects on the Na-ATPase which occur in the absence of intracellular ADP in human red blood cells.

摘要

Na⁺和K⁺跨细胞质膜的偶联主动转运由（Na⁺ + K⁺）刺激的Mg²⁺依赖性ATP酶介导。这种钠泵的主动阳离子转运涉及该酶由细胞内ATP进行的循环性钠依赖性磷酸化以及由K⁺刺激的磷酸酶的水解去磷酸化（参考文献1）。在人类红细胞、骨骼肌和乌贼轴突中，用Na替换细胞外K会导致对哇巴因敏感的Na外流，并伴有细胞外Na的内流。显然没有净Na移动，也没有ATP的净水解。Na:Na交换速率受ADP水平升高的刺激，在细胞内ATP完全耗尽的细胞中未观察到交换转运。这些特征表明，钠泵的Na交换模式背后的生化机制涉及ATP对酶的磷酸化（这需要细胞内Na），随后由ADP使其去磷酸化。在从多种来源部分纯化的（Na⁺ + K⁺）ATP酶中观察到了这样的反应，并且已经描述了其对Na浓度的依赖性（尽管之前未针对红细胞酶）。在本研究中，在含有笼装ATP的血影在350nm处短暂照射后，通过光释放的ATP引发细胞内ATP:ADP交换反应。随后的ATP:ADP交换反应中对哇巴因敏感的成分对细胞外Na表现出双相反应。0 - 10 mM范围内的外部Na具有抑制作用，而超过此范围增加浓度会以大致线性方式刺激交换速率，直至100 mM Na。这些结果首次直接证明了Na对整个酶循环中这一局部序列作用的方向性，并且在定性上类似于在人类红细胞中不存在细胞内ADP时Na对钠 - ATP酶的影响。