Department of Plant Biology, USDA/ARS, University of Illinois, 61801, Urbana, IL, USA.
Photosynth Res. 1987 Jan;12(1):43-62. doi: 10.1007/BF00019150.
The problem of predicting the kinetics of proton efflux and the decay of the internal proton concentration for vesicles containing one or more buffers for which the internal proton concentration is initially higher than that of the surrounding medium is examined. An analytical solution is derived that describes the time course of the proton efflux from vesicles and the decay of the internal proton concentration under conditions of zero transmembrane electric potential. The effect of the internal buffers is to increase the time required for the proton concentration gradient to equilibrate across the membrane. To simplify the analysis we assume that the equilibration of the internal and external proton activity is due primarily to proton diffusion through the membrane, and not to hydroxyl ion flux. For a vesicle containing a single buffer the solution requires six independent physical parameters: the initial internal proton concentration, the external proton concentration, the ratio of the vesicle surface area to the internal volume, the permeability coefficient of the membrane for protons, the total concentration of the internal buffer, and the equilibrium constant for the dissociation of the internal buffer. Determination of these physical values is sufficient to predict the time dependence of the internal proton concentration and of the proton efflux. Over a pH range that is below or near the pK of the internal buffer the solution is complex. However, if the initial pH is one unit or more higher than the pK of the internal buffer the kinetics of the internal proton concentration and proton efflux can be described by a pseudo first order reaction. In this case the apparent rate constant depends linearly on the permeability coefficient and is dominated by the total internal buffer concentration and its pK. For example, increasing the internal buffer concentration inside a vesicle by 10-fold results in an approximately 10-fold increase in the half-time of the proton efflux kinetics. The theoretical analysis is applied to thylakiod vesicles using experimentally determined values for the physical parameters. The predictions of the analysis are compared to experimentally observed kinetics.
研究了含有一个或多个缓冲液的囊泡中质子外溢和内部质子浓度衰减的动力学预测问题，其中缓冲液的内部质子浓度最初高于周围介质。推导了一个描述零跨膜电动势能下质子从囊泡中流出和内部质子浓度衰减的时间过程的解析解。内部缓冲液的作用是增加质子浓度梯度在膜两侧平衡所需的时间。为了简化分析，我们假设内部和外部质子活度的平衡主要是由于质子通过膜扩散，而不是羟基离子通量。对于含有单个缓冲液的囊泡，该解需要六个独立的物理参数：初始内部质子浓度、外部质子浓度、囊泡表面积与内部体积之比、膜对质子的渗透系数、内部缓冲液的总浓度以及内部缓冲液离解的平衡常数。这些物理值的确定足以预测内部质子浓度和质子外溢的时间依赖性。在低于或接近内部缓冲液 pK 的 pH 范围内，该解是复杂的。然而，如果初始 pH 值比内部缓冲液的 pK 值高一个单位或更多，则内部质子浓度和质子外溢的动力学可以用拟一级反应来描述。在这种情况下，表观速率常数与渗透系数线性相关，主要由总内部缓冲浓度及其 pK 决定。例如，将囊泡内部的内部缓冲浓度增加 10 倍，质子外溢动力学的半衰期会增加约 10 倍。该理论分析应用于类囊体囊泡，使用实验确定的物理参数值。将分析的预测与实验观察到的动力学进行了比较。
