KINETIC STUDY OF NA PUMP IN RED-CELLS - ITS RELEVANCE TO MECHANISM OF ACTIVE-TRANSPORT
KINETIC STUDY OF NA PUMP IN RED-CELLS - ITS RELEVANCE TO MECHANISM OF ACTIVE-TRANSPORT
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DOI：
10.1111/j.1749-6632.1974.tb19108.x
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发表时间：
1974-01-01
影响因子：
5.2
通讯作者：
GARAY, RP
中科院分区：
文献类型：
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作者：
GARRAHAN, PJ;GARAY, RP
更好地理解由Na泵催化的Na或K的主动运动的机制的可能方法之一是观察这些运动与细胞内或细胞外介质中阳离子浓度的依赖性。这类研究已经大大有利于程序的发展，使红细胞的细胞内组成在很大范围内变化。通过Na泵的阳离子通量的动力学研究可以用两种相当不同的方法来进行。第一个是当阳离子浓度在细胞膜的一个表面上变化而在相对表面上保持恒定时，观察通量与阳离子浓度的曲线。从这些曲线的形状，我们可以获得关于阳离子结合位点的数量、它们的表观亲和力、它们的相互作用等的间接信息。2y3但是，无论这些研究多么有用，它们都受到这样一个事实的阻碍，即几乎总是有一个以上的动力学方案符合实验结果。替代模型之间的区别超出了动力学的范围，只有当测量阳离子与纯化的ATP酶制剂结合的程序变得可用时，才可能成为可能。使用动力学方法研究Na泵机制的另一种方法是观察细胞膜一个表面上的阳离子组成的变化对细胞膜相对表面上的阳离子通量与阳离子组成相关的曲线形状的影响。[4]我们现在想对采用第二种方法在人体红细胞中进行的实验结果进行评论，并表明它们对Na泵的假设方案设置了一组相当严格的限制。
One of the possible approaches to understand better the mechanism responsible of the active movements of Na or K catalyzed by the Na pump is to look at the dependence of these movements with the concentration of cations in the intraor extracellular media. This sort of study has been greatly favored by the development of procedures that allow the intracellular composition of red cells to vary within a wide range.'The study of the kinetics of cation fluxes through the Na pump can be approached in two rather different ways. The first is to look at the flux vs. cation concentration curves when cation concentration is varied at one of the surfaces and kept constant at the opposite surface of the cell membrane. From the shape of these curves we can obtain indirect information on the number of cation binding sites, their apparent affinities, their interactions, and the like. 2y3 But, however useful these studies may be, they are hampered by the fact that almost always more than one kinetic scheme will fit the experimental results. The distinction between alternative models lies beyond the realm of kinetics and probably will become possible only when procedures to measure the binding of cations to purified ATPase preparations become available. Another way of using the kinetic approach to study the mechanism of the Na pump is to look at the effect that changes in the cation composition at one of the surfaces of the cell membrane have on the shape of the curves relating cation flux with cation composition at the opposite surface of the cell membrane. 4 We would like to comment now on the results of experiments performed in human red cells in which the second approach was employed, and to show that they place a set of rather stringent restrictions on the hypothetical schemes of the Na pump.