The relationship between the electrochemical proton gradient and active transport in Escherichia coli membrane vesicles.
The relationship between the electrochemical proton gradient and active transport in Escherichia coli membrane vesicles.
复制标题
电化学质子梯度与大肠杆菌膜囊泡主动运输之间的关系。
作者：
S. Ramos;H. Kaback
在前一篇论文[拉莫斯，S.，和卡巴克，H. R.（1977），Biochemistry 16（本期的前一篇论文）]，证明了大肠杆菌膜囊泡在适当条件下产生大的电化学质子梯度（delta-muH+），并且delta-muH+及其分力的一些性质[即，膜电位（Δ psi）和质子的化学梯度（Δ PH）]。在本文中，之间的关系Δ-μ H+，Δ psi，和Δ PH和特定溶质的主动运输进行检查。将乳糖或葡萄糖6-磷酸添加到含有适当转运系统的膜囊泡中，导致deltapH部分塌陷，为呼吸能量可以通过跨膜pH梯度驱动主动转运的建议提供了直接证据。用缬氨霉素和尼日利亚菌素进行的滴定研究得出的结论是，在pH 5.5时，存在两种一般类型的转运系统：主要由Δ-muH+驱动的转运系统（乳糖、脯氨酸、丝氨酸、甘氨酸、酪氨酸、谷氨酸、亮氨酸、赖氨酸、半胱氨酸和琥珀酸）和主要由Δ PH驱动的转运系统（葡萄糖6-磷酸、D-乳酸、葡萄糖醛酸和葡萄糖酸）。然而，重要的是，它也表明，在pH值7.5，所有这些运输系统是由Δ psi，其中包括唯一的组件的Δ-μ H+在此外部pH值。此外，外部pH值的影响上的稳态水平的积累不同的溶质进行检查，它表明，没有pH值的配置文件对应于那些观察到的Δ-μ H+，Δ psi，或Δ PH值。此外，在外部pH值高于6.0-6.5时，Δ-μ H+不足以解释为每种底物建立的浓度梯度，除非质子和累积溶质之间的化学计量大于1。这些结果证实了化学渗透假说的许多方面，但它们也在某些重要方面扩展了这一概念，并允许解释一些早期的观察结果，这些观察结果似乎排除了化学渗透现象参与主动运输。
In the previous paper [ramos, S., and Kaback, H.R. (1977), Biochemistry 16 (preceding paper in this issue)], it was demonstrated that Escherichia coli membrane vesicles generate a large electrochemical proton gradient (delta-muH+) under appropriate conditions, and some of the properties of delta-muH+ and its component forces [i.e., the membrane potential (delta psi) and the chemical gradient of protons (deltapH)] were described. In this paper, the relationship between delta-muH+, delta psi, and deltapH and the active transport of specific solutes is examined. Addition of lactose or glucose 6-phosphate to membrane vesicles containing the appropriate transport systems results in partial collapse of deltapH, providing direct evidence for the suggestion that respiratory energy can drive active transport via the pH gradient across the membrane. Titration studies with valinomycin and nigericin lead to the conclusion that, at pH 5.5, there are two general classes of transport systems: those that are driven primarily by delta-muH+ (lactose, proline, serine, glycine, tyrosine, glutamate, leucine, lysine, cysteine, and succinate) and those that are driven primarily by deltapH (glucose 6-phosphate, D-lactate, glucuronate, and gluconate). Importantly, however, it is also demonstrated that at pH 7.5, all of these transport systems are driven by delta psi which comprises the only component of delta-muH+ at this external pH. In addition, the effect of external pH on the steady-state levels of accumulation of different solutes is examined, and it is shown that none of the pH profiles correspond to those observed for delta-muH+, delta psi, or deltapH. Moreover, at external pH values above 6.0-6.5, delta-muH+ is insufficient to account for the concentration gradients established for each substrate unless the stoichiometry between protons and accumulated solutes is greater than unity. The results confirm many facets of the chemiosmotic hypothesis, but they also extend the concept in certain important respects and allow explanations for some earlier observations which seemed to preclude the involvement of chemiosmotic phenomena in active transport.