INTERPRETATION OF CURRENT-VOLTAGE RELATIONSHIPS FOR ACTIVE ION-TRANSPORT SYSTEMS .1. STEADY-STATE REACTION-KINETIC ANALYSIS OF CLASS-I MECHANISMS
INTERPRETATION OF CURRENT-VOLTAGE RELATIONSHIPS FOR ACTIVE ION-TRANSPORT SYSTEMS .1. STEADY-STATE REACTION-KINETIC ANALYSIS OF CLASS-I MECHANISMS
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DOI：
10.1007/bf01870979
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发表时间：
1981-01-01
影响因子：
2.4
通讯作者：
SLAYMAN, CL
中科院分区：
文献类型：
--
作者：
HANSEN, UP;GRADMANN, D;SLAYMAN, CL
本文建立了一个简单的反应动力学模型来描述离子的生电泵送和共（或逆）输运。它使用标准的稳态方法循环酶或载体介导的运输，但不承担任何特定的反应步骤的速率限制。在Lauger和Stark的建议之后，通过对称的Eyring势垒引入了电压依赖性。为了解释电流-电压关系（I-V），所有与电压无关的反应步骤都集中在一起，因此最简单形式的模型可以描述为伪2态模型。它的特点是由2个电压依赖的反应常数，2个集总的电压无关的反应常数和2个储备因子，正式考虑到载流子状态，是无法区分的分析。该模型产生了广泛的I-V关系，这取决于4个反应常数的相对大小，足以描述基本上所有的I-V数据，现在可用的活性离子传输系统。代数和数值分析的储备因子，通过扩展的伪3，4和5-状态模型，表明它们是有界的，而不是大的集总途径中的反应常数的大多数组合。这一规则的最重要的例外发生时，载体放电立即跟随电荷传输的膜，是非常快的相对于其他成分的电压无关的反应。这种情况产生化学和电梯度的动力学等效性，从而提供离子动力的一致定义（例如，质子动力，PMF）。在适当的限制下，它还产生净运输速度与膜电位或PMF之间的线性和对数线性关系。因此，该模型适应质子传输系统的许多已知的属性，特别是在化学渗透或能量耦合膜中观察到的。
This paper develops a simple reaction kinetic model to describe electrogenic pumping and co- (or counter-) transport of ions. It uses the standard steady-state approach for cyclic enzyme- or carrier-mediated transport, but does not assume rate limitation by any particular reaction step. Voltage-dependence is introduced, after the suggestion of Lauger and Stark, via a symmetric Eyring barrier. For interpretation of current-voltage relationships (I-V), all voltage-independent reaction steps are lumped together, so the model in its simplest form can be described as a pseudo-2-state model. It is characterized by the 2 voltage-dependent reaction constants, 2 lumped voltage-independent reaction constants and 2 reserve factors, which formally take account of carrier states that are indistinguishable in the analysis. The model generates a wide range of I-V relationships, depending on the relative magnitudes of the 4 reaction constants, sufficient to describe essentially all I-V data now available on active ion-transport systems. Algebraic and numerical analysis of the reserve factors, by means of expanded pseudo-3, 4 and 5-state models, shows them to be bounded and not large for most combinations of reaction constants in the lumped pathway. The most important exception to this rule occurs when carrier decharging immediately follows charge transit of the membrane and is very fast relative to other constituent voltage-independent reactions. Such a circumstance generates kinetic equivalence of chemical and electrical gradients, thus providing a consistent definition of ion-motive forces (e.g., proton-motive force, PMF). With appropriate restrictions, it also yields both linear and log-linear relationships between net transport velocity and either membrane potential or PMF. The model thus accommodates many known properties of proton-transport systems, particularly as observed in chemiosmotic or energy-coupling membranes.