A model of Na-K-2Cl cotransport based on ordered ion binding and glide symmetry
A model of Na-K-2Cl cotransport based on ordered ion binding and glide symmetry
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DOI：
10.1152/ajpcell.1998.274.2.c299
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发表时间：
1998-02-01
影响因子：
5.5
通讯作者：
Haas, M
中科院分区：
文献类型：
--
作者：
Lytle, C;McManus, TJ;Haas, M
在鸭红细胞中，Na-K-2Cl 共转运表现出两种离子运动模式：净共转运和专性阳离子交换。在高 K 细胞中，主要的交换是 WK（或 K/Rb）。在高钠电池中，它变成Na/Na（或Na/Li）。两者都代表部分反应，其中满载的载体释放其部分货物，重新结合新鲜离子，并满载地穿过膜返回。当载体完全卸载并空载返回时，就会发生净协同运输。在所有测试条件下，该模式具有 1Na:1K:2Cl 的固定化学计量。两种交换的离子要求不同：K/K 交换仅需要外部的 K 和 Cl，但内部需要所有三种离子。 Na/Na 交换需要所有三个离子在外部，但只有 Na 在内部。我们提出了一个简单的模型，其中载体只能在满载或完全空时移动，并且离子以严格有序的顺序结合。例如，在外部，Na 首先结合，然后是 Cl，随后是 K 和第二个 Cl。在内部，先打开后关闭（滑移对称），因此首先释放 Na，然后释放第一个 Cl，然后释放 K，最后释放第二个 Cl。只有这样，空的形式才能返回到外部，开始新的循环。
In the duck red blood cell, Na-K-2Cl cotransport exhibits two modes of ion movement: net cotransport and obligate cation exchange. In high-K cells, the predominant exchange is WK (or K/Rb). In high-Na cells, it becomes Na/Na (or Na/Li). Both represent partial reactions in which a fully loaded carrier releases part of its cargo, rebinds fresh ions, and returns back across the membrane fully loaded. Net cotransport occurs when the carrier unloads completely and returns empty. This mode has a fixed stoichiometry of 1Na:1K:2Cl under all conditions tested. The ion requirements of the two exchanges differ: K/K exchange requires only K and Cl outside but all three ions inside. Na/Na exchange requires all three ions outside but only Na inside. We propose a simple model in which the carrier can only move when either fully loaded or completely empty and in which the ions bind in a strictly ordered sequence. For example, externally, a Na binds first and then a Cl, followed by a K and a second Cl. Internally, the first on is the first off (glide symmetry), so the Na is released first and then the first Cl, followed by the K and finally by the second Cl. Only then can the empty form return to the outside to start a new cycle.