Bullock J O, Kolen E R, Shear J L
Department of Physiology, University of Missouri-Columbia 65212.
J Membr Biol. 1992 May;128(1):1-16. doi: 10.1007/BF00231866.
Channels formed by colicin E1 in planar lipid bilayers have large diameters and conduct both cations and anions. The rates at which ions are transported, however, are relatively slow, and the relative anion-to-cation selectivity is modulated over a wide range by the pH of the bathing solutions. We have examined the permeability of these channels to cationic probes having a variety of sizes, shapes, and charge distributions. All of the monovalent probes were found to be permeant, establishing a minimum diameter at the narrowest part of the pore of approximately 9 A. In contrast to this behavior, all of the polyvalent organic cations were shown to be impermeant. This simple exclusionary rule is interpreted as evidence that, when steric restrictions require partial dehydration of an ion, the structure of the channel is able to provide a substitute electrostatic environment for only one charged group at time.
由大肠杆菌素E1在平面脂质双分子层中形成的通道具有较大的直径，能传导阳离子和阴离子。然而，离子的运输速率相对较慢，并且相对阴离子与阳离子的选择性会受到浴液pH值的广泛调节。我们研究了这些通道对具有各种尺寸、形状和电荷分布的阳离子探针的通透性。发现所有单价探针都是可通透的，在孔最窄处确定了约9埃的最小直径。与这种行为相反，所有多价有机阳离子都显示为不可通透的。这种简单的排除规则被解释为这样的证据：当空间限制要求离子部分脱水时，通道结构一次仅能为一个带电基团提供替代的静电环境。
