Vachon V, Laprade R, Coulton J W
Biochim Biophys Acta. 1986 Sep 25;861(1):74-82. doi: 10.1016/0005-2736(86)90373-1.
The major outer membrane protein (40 kDa) of the bacterium Haemophilus influenzae type b is a porin which forms transmembrane permeability channels. It has an exclusion limit for oligosaccharides of about 1.4 kDa. When this protein was added to the aqueous phase which was bathing a planar lipid bilayer, it caused the conductance of the membrane to increase by several orders of magnitude. At low protein concentrations (2-10 pM), the conductance of the membrane increased in a stepwise fashion with an average single-channel conductance of 1.1 nS in 1 M KCl. Single-channel experiments were performed with a variety of different salts. The conductance of single channels was proportional to the specific conductance of the aqueous solution which was bathing the membrane. Current through the pores was proportional to the applied voltage, indicating that these pores are not voltage-controlled. The 40 kDa porin was very slightly cation-selective: the pores were about 1.6-times more permeable to potassium ions than to chloride ions. These properties of the 40 kDa porin are those of large water-filled channels and are characteristic of most bacterial porins. The single-channel conductance of the porin is, however, much smaller than might be expected from its exclusion limit. A model is proposed which could explain the differences in apparent pore size.
b型流感嗜血杆菌的主要外膜蛋白（40 kDa）是一种孔蛋白，可形成跨膜通透性通道。它对寡糖的排阻极限约为1.4 kDa。当将这种蛋白添加到浸泡平面脂质双层的水相中时，会使膜的电导率增加几个数量级。在低蛋白浓度（2 - 10 pM）下，膜的电导率呈阶梯式增加，在1 M KCl中平均单通道电导率为1.1 nS。使用多种不同的盐进行了单通道实验。单通道的电导率与浸泡膜的水溶液的比电导率成正比。通过孔的电流与施加的电压成正比，表明这些孔不受电压控制。40 kDa孔蛋白对阳离子有非常轻微的选择性：这些孔对钾离子的通透性比对氯离子高约1.6倍。40 kDa孔蛋白的这些特性是大的充满水的通道的特性，也是大多数细菌孔蛋白的特征。然而，孔蛋白的单通道电导率比根据其排阻极限预期的要小得多。提出了一个模型来解释表观孔径的差异。
