Nestorovich Ekaterina M, Rostovtseva Tatiana K, Bezrukov Sergey M
Laboratory of Physical and Structural Biology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-0924, USA.
Biophys J. 2003 Dec;85(6):3718-29. doi: 10.1016/S0006-3495(03)74788-2.
Single trimeric channels of the general bacterial porin, OmpF, were reconstituted into planar lipid membranes and their conductance, selectivity, and open-channel noise were studied over a wide range of proton concentrations. From pH 1 to pH 12, channel transport properties displayed three characteristic regimes. First, in acidic solutions, channel conductance is a strong function of pH; it increases by approximately threefold as the proton concentration decreases from pH 1 to pH 5. This rise in conductance is accompanied by a sharp increase in cation transport number and by pronounced open-channel low-frequency current noise with a peak at approximately pH 2.5. Random stepwise transients with amplitudes at approximately 1/5 of the monomer conductance are major contributors to this noise. Second, over the middle range (pH 5/pH 9), channel conductance and selectivity stay virtually constant; open channel noise is at its minimum. Third, over the basic range (pH 9/pH 12), channel conductance and cation selectivity start to grow again with an onset of a higher frequency open-channel noise. We attribute these effects to the reversible protonation of channel residues whose pH-dependent charge influences transport by direct interactions with ions passing through the channel.
将普通细菌孔蛋白OmpF的单个三聚体通道重构到平面脂质膜中，并在广泛的质子浓度范围内研究其电导率、选择性和开放通道噪声。从pH 1到pH 12，通道传输特性呈现出三种特征状态。首先，在酸性溶液中，通道电导率是pH的强函数；随着质子浓度从pH 1降低到pH 5，电导率增加约三倍。电导率的这种升高伴随着阳离子转运数的急剧增加以及明显的开放通道低频电流噪声，其峰值出现在约pH 2.5处。幅度约为单体电导率1/5的随机逐步瞬变是这种噪声的主要贡献者。其次，在中间范围（pH 5/pH 9）内，通道电导率和选择性几乎保持恒定；开放通道噪声处于最低水平。第三，在碱性范围（pH 9/pH 12）内，通道电导率和阳离子选择性随着高频开放通道噪声开始再次增加。我们将这些效应归因于通道残基的可逆质子化，其pH依赖性电荷通过与穿过通道的离子直接相互作用来影响运输。
