Antonenko Y N, Pohl P
A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russian Federation.
Biochim Biophys Acta. 1995 Apr 12;1235(1):57-61. doi: 10.1016/0005-2736(94)00274-s.
Catalytic reactions in the unstirred layers near bilayer lipid membranes can induce nonmonotonic concentration profiles near the membrane surface. In the case of transmembrane diffusion of a substrate immediately followed by its conversion due to the presence of an aqueous soluble enzyme the size of the unstirred layer defined in terms of the concentration gradient at the membrane surface does not correspond to the width of the aqueous layer adjacent to the membrane where the concentration differs from the bulk phase concentration. Deducing of flux values or convection parameters from the concentration gradient at zero distance from the membrane gives misleading results. An empirical equation for the estimation of the size of the concentration boundary layer is proposed. It was derived from pH profiles registered with the help of a microelectrode near a planar bilayer lipid membrane surrounded by a buffer solution containing at one side of the membrane acetaldehyde and sodium acetate and at the other side alcohol dehydrogenase. Since this parameter equals to the thickness of the unstirred layer in the case of exponential concentration profiles it may be applied to estimate both mass transfer restrictions and kinetic of diffusion limited reactions occurring in the immediate membrane vicinity regardless the complexity of the system under investigation.
双层脂质膜附近未搅拌层中的催化反应可在膜表面附近诱导非单调浓度分布。对于底物跨膜扩散后紧接着由于水溶性酶的存在而发生转化的情况，根据膜表面浓度梯度定义的未搅拌层大小与膜相邻水层的宽度不对应，在该水层中浓度与本体相浓度不同。从距膜零距离处的浓度梯度推导通量值或对流参数会得出误导性结果。提出了一个用于估计浓度边界层大小的经验方程。它是根据借助微电极记录的pH分布推导出来的，该微电极位于平面双层脂质膜附近，膜的一侧被含有乙醛和醋酸钠的缓冲溶液包围，另一侧被乙醇脱氢酶包围。由于在指数浓度分布情况下该参数等于未搅拌层的厚度，因此它可用于估计传质限制以及在膜紧邻区域发生的扩散限制反应的动力学，而不管所研究系统的复杂性如何。
