Chiu S W, Subramaniam S, Jakobsson E
National Center for Supercomputing Applications, University of Illinois, Urbana, Illinois 61801, USA.
Biophys J. 1999 Apr;76(4):1939-50. doi: 10.1016/S0006-3495(99)77353-4.
A gramicidin channel in a fluid phase DMPC bilayer with excess lipid and water has been simulated. By use of the formal correspondence between diffusion and random walk, a permeability for water through the channel was calculated, and was found to agree closely with the experimental results of Rosenberg and Finkelstein (Rosenberg, P.A., and A. Finkelstein. 1978. J. Gen. Physiol. 72:327-340; 341-350) for permeation of water through gramicidin in a phospholipid membrane. By using fluctuation analysis, components of resistance to permeation were computed for movement through the channel interior, for the transition step at the channel mouth where the water molecule solvation environment changes, and for the process of diffusion up to the channel mouth. The majority of the resistance to permeation appears to occur in the transition step at the channel mouth. A significant amount is also due to structurally based free energy barriers within the channel. Only small amounts are due to local friction within the channel or to diffusive resistance for approaching the channel mouth.
已对处于具有过量脂质和水的流体相二肉豆蔻酰磷脂酰胆碱（DMPC）双层中的短杆菌肽通道进行了模拟。通过利用扩散与随机游走之间的形式对应关系，计算了水通过该通道的渗透率，发现其与罗森伯格和芬克尔斯坦（罗森伯格，P.A.，以及A.芬克尔斯坦。1978年。《普通生理学杂志》72:327 - 340；341 - 350）关于水在磷脂膜中通过短杆菌肽的渗透实验结果密切相符。通过波动分析，计算了水通过通道内部移动、在通道口水分子溶剂化环境发生变化的过渡步骤以及扩散至通道口过程中的渗透阻力分量。大部分渗透阻力似乎发生在通道口的过渡步骤。相当一部分阻力也归因于通道内基于结构的自由能屏障。只有少量阻力是由于通道内的局部摩擦或接近通道口的扩散阻力。
