THE OVERSHOOT PHENOMENON IN COTRANSPORT
THE OVERSHOOT PHENOMENON IN COTRANSPORT
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DOI：
10.1016/0005-2736(84)90253-0
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发表时间：
1984-01-01
期刊：
影响因子：
--
通讯作者：
WEINSTEIN, AM
中科院分区：
文献类型：
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作者：
HEINZ, E;WEINSTEIN, AM
基于简化的方程，用计算机模拟了中性底物（糖或氨基酸）的Na+连接共转运的超调曲线。该方法考虑了膜电位差的影响，并建立了峰高与某些转运参数（如最大速率、三元复合物解离常数、转运体电荷）之间的定量关系。此外，它测试了2个替代模型的速率决定步骤：易位，一方面，和关联/解离的配体在易位位点，另一方面。过冲可以获得类似于通常发现的实验，提供的最大速率和转运和溶质运输之间的亲和力超过一定的最小值。过冲效应与钠连接的共转运增强负膜电位（内部相对于外部）和减少正电位。在第一种情况下，峰值更高并且发生得更快。在后一种情况下，峰值较低且延迟。电位差对过冲曲线的影响并不明显取决于空易位体的电荷，除非后者的易位具有强烈的限速作用。为了获得过冲曲线，与先前的假设相反，易位步骤不必是速率限制的。
Based on simplified equations, the overshoot curve experimentally observed with Na+-linked cotransport of neutral substrate (sugars or amino acids) was simulated by computer. The approach includes the effect of electrical membrane potential difference, and the quantitative relationship between height of peak and certain transport parameters, such as maximum rate, dissociation constant of ternary complex, electric charge of translocator, respectively. In addition, it tests 2 alternative models with respect to the rate-determining step: the translocation, on the one hand, and the association/dissociation of the ligands at the translocator site, on the other. An overshoot can be obtained similar to that usually found experimentally, provided that maximum rate and affinity between translocator and transport of solute exceed certain minimum values. The overshoot effect with Na-linked cotransport is enhanced by a negative membrane potential (inside relative to outside) and decreased by a positive potential. In the first case, the peak is higher and occurs faster. In the latter case, the peak is lower and delayed. The effect of an electric potential difference on the overshoot curve does not depend appreciably on the charge of the empty translocator, except if the translocation of the latter is strongly rate-limiting. To obtain an overshoot curve, it is not necessary that the translocation step be rate-limiting, contrary to what was postulated previously.