Hartsel S C, Cafiso D S
Biochemistry. 1986 Dec 16;25(25):8214-9. doi: 10.1021/bi00373a014.
A new series of negatively charged, paramagnetic alkylsulfonate probes was synthesized and can be used to measure both the internal and the external surface potentials of model membrane systems. We tested for discreteness-of-charge effects in lipid membranes by comparing the surface potentials, estimated by use of these negatively charged amphiphiles, with that of a series of positively charged alkylammonium nitroxides in charged membranes. From the partitioning of these probes, the membrane surface potential was estimated in phosphatidylcholine membranes containing either phosphatidylserine or didodecyldimethylammonium bromide. The surface potentials, estimated with either positive or negative probes, were identical, within experimental error, in either positive or negative membranes, and they were well accounted for by a simple Gouy-Chapman-Stern theory. This symmetry, with respect to the sign of the charge, indicates that discreteness-of-charge effects are not significant in determining the potential-sensitive phase partitioning of these probes in model membranes. Thus, despite the fact that charge on membranes is discrete, models that assume a uniform density of charge in the plane of the membrane adequately account for the potentials measured by these amphiphilic probes.
合成了一系列新的带负电荷的顺磁性烷基磺酸盐探针，可用于测量模型膜系统的内表面和外表面电位。我们通过比较使用这些带负电荷的两亲物估算的表面电位与一系列带正电荷的烷基铵氮氧化物在带电膜中的表面电位，来测试脂膜中的电荷离散效应。根据这些探针的分配情况，在含有磷脂酰丝氨酸或十二烷基二甲基溴化铵的磷脂酰胆碱膜中估算膜表面电位。在正膜或负膜中，用正探针或负探针估算的表面电位在实验误差范围内是相同的，并且简单的古伊-查普曼-斯特恩理论能很好地解释这些结果。这种关于电荷符号的对称性表明，电荷离散效应在确定这些探针在模型膜中的电位敏感相分配时并不显著。因此，尽管膜上电荷是离散的，但假设膜平面内电荷密度均匀的模型足以解释这些两亲性探针测量的电位。
