Benz R, Ishii J, Nakae T
J Membr Biol. 1980 Aug 21;56(1):19-29. doi: 10.1007/BF01869348.
The three types of porin (matrix-proteins) from Salmonella typhimurium with molecular weights of 38,000, 39,000 and 40,000 were reconstituted with lipid bilayer membranes either as a trimer or as an oligomer (complex I). The specific conductance of the membranes increased several orders of magnitude after the addition of the porins into the aqueous phase bathing the membranes. A linear relationship between protein concentration in the aqueous phase and membrane conductance was found. In the case of lower protein concentrations (10)(-12)M), the conductance increased in a stepwise fashion with a single conductance increment of 2.3 nS in 1 M KC1. For a given salt the conductance increment was found to be largely independent of the particular porin (38 K, 39 K or 40 K) and on the state of aggregation, although porin oligomers showed an up to 10 times smaller conductance increase in macroscopic conductance measurements. The conductance pathway has an ohmic current voltage characteristic and a poor selectivity for different alkali ions. Further information on the structure of the pores formed by the different porins from Salmonella was obtained from the selectivity for various ions. From the permeability of the pore for large ions (Tris+, glucosamine+, Hepes-) a minimum pore diameter of 0.8 nm is estimated. This value is in agreement with the size of the pore as calculated from the conductance data for 1 M KC1 (1.4 nm for a pore length of 7.5 nm). The pore diameter may well account for the sugar permeability which has been found in reconstituted vesicles. The findings reported here are consistent with the assumption that the different porins form large aqueous channels in the lipid bilayer membranes and that the single conductance unit is a trimer. In addition, it is suggested that one trimer contains only one pore rather than a bundle of pores.
鼠伤寒沙门氏菌的三种分子量分别为38,000、39,000和40,000的孔蛋白（基质蛋白），以三聚体或寡聚体（复合体I）的形式与脂质双分子层膜进行了重构。将孔蛋白添加到浸泡膜的水相中后，膜的比电导率增加了几个数量级。发现水相中蛋白质浓度与膜电导率之间存在线性关系。在较低蛋白质浓度（10⁻¹²M）的情况下，电导率以逐步方式增加，在1M KCl中单次电导率增量为2.3 nS。对于给定的盐，尽管在宏观电导率测量中孔蛋白寡聚体的电导率增加幅度小至10倍，但发现电导率增量在很大程度上与特定的孔蛋白（38K、39K或40K）以及聚集状态无关。电导途径具有欧姆电流电压特性，对不同碱金属离子的选择性较差。通过对各种离子的选择性，获得了关于鼠伤寒沙门氏菌不同孔蛋白形成的孔结构的更多信息。根据孔对大离子（Tris⁺、葡糖胺⁺、Hepes⁻）的通透性，估计最小孔径为0.8nm。该值与根据1M KCl的电导率数据计算出的孔尺寸（孔长7.5nm时为1.4nm）一致。孔径很可能解释了在重构囊泡中发现的糖通透性。此处报道的发现与以下假设一致：不同的孔蛋白在脂质双分子层膜中形成大的水通道，并且单个电导单位是三聚体。此外，有人提出一个三聚体仅包含一个孔而不是一束孔。
