Fuks B, Homblé F
Laboratoire de Physiologie Végétale, Faculté des Sciences, Université Libre de Bruxelles, Belgium.
Biophys J. 1994 May;66(5):1404-14. doi: 10.1016/S0006-3495(94)80931-2.
Electrical measurements were carried out on planar lipid membranes from thylakoid lipids. The specific capacitance of membranes formed from decane-containing monogalactosyldiacylglycerol (MGDG), which accounts for 57% of the total lipid content of thylakoids, showed that it adopted a bilayer structure. Solvent-free bilayers of MGDG were not formed, with very rare exceptions, indicating that decane is required to stabilize the planar conformation. However, this cone-shaped lipid produces bilayer structures in combination with other cylindrical thylakoid lipids even in the absence of organic solvent. We compared the properties of solvent-free and decane-containing bilayers from MGDG, soybean lecithin, and the quaternary mixture of lipids similar to that found in vivo. The conductance of decane-MGDG was 26 times higher than that of decane-lecithin. The flux through the decane-lecithin bilayer was found to be slightly dependent on pH, whereas the decane-MGDG membrane was not. The specific conductance of bilayers formed from the quaternary mixture of lipids was 5 to 10 times larger than lecithin (with alkane or not). Further experiments with bilayers made in the presence of a KCl gradient showed that decane-MGDG, decane-MGDG/DGDG/SQDG/PG, and solvent-free MGDG/DGDG/SQDG/PG were cation-selective. The permeability coefficient for potassium ranged from 4.9 to 8.3 x 10(-11) cm s-1. The permeability coefficient for protons in galactolipids, however, was determined to be about six orders of magnitude higher than the value for potassium ions. The HCl permeation mechanism through the lipid membranes was determined from diffusion potentials measured in HCl gradients. Our results suggest that HCl was not transported as neutral molecules. The data is discussed with regard to the function of galactolipids in the ion transport through thylakoid membranes.
对类囊体脂质构成的平面脂质膜进行了电学测量。由含癸烷的单半乳糖二酰基甘油（MGDG）形成的膜的比电容表明其呈现双层结构，MGDG占类囊体总脂质含量的57%。除了极少数例外情况，未形成无溶剂的MGDG双层，这表明需要癸烷来稳定平面构象。然而，这种锥形脂质即使在没有有机溶剂的情况下，与其他圆柱形类囊体脂质结合也会产生双层结构。我们比较了MGDG、大豆卵磷脂以及类似于体内发现的脂质四元混合物的无溶剂和含癸烷双层的性质。癸烷-MGDG的电导率比癸烷-卵磷脂高26倍。发现通过癸烷-卵磷脂双层的通量略微依赖于pH值，而癸烷-MGDG膜则不然。由脂质四元混合物形成的双层的比电导率比卵磷脂（有无烷烃）大5至10倍。在存在KCl梯度的情况下对双层进行的进一步实验表明，癸烷-MGDG、癸烷-MGDG/DGDG/SQDG/PG和无溶剂的MGDG/DGDG/SQDG/PG具有阳离子选择性。钾的渗透系数范围为4.9至8.3×10⁻¹¹厘米/秒。然而，确定半乳糖脂中质子的渗透系数比钾离子的值高约六个数量级。通过在HCl梯度中测量的扩散电位确定了HCl通过脂质膜的渗透机制。我们的结果表明，HCl不是以中性分子形式运输的。结合半乳糖脂在通过类囊体膜的离子运输中的功能对数据进行了讨论。
