Transport of Endocrine Disruptors in Phospholipid Bilayer Membranes

首次利用核磁共振分析了内分泌干扰物（ED）在磷脂双层膜中的转运过程。直接测定了ED、双酚A （BPA）和4-辛基酚（OP）的自扩散速率，并与在水中的自扩散速率进行了比较。同时监测膜中脂质基质的动态，而不标记细胞核。它的成功归功于一个特殊设计的高功率、高灵敏度探头。这种新型探针可以施加足够大的磁场梯度来监测高粘性脂质膜中的动态事件。将该探针与高分辨率600 MHz核磁共振仪结合，我们展示了BPA、OP和脂类在膜中的移动速度，以及ED迁移率与膜脂动力学的关系。同时还研究了ED迁移率与在膜中的位置的关系。ED在膜中的传递速度并不快，但比溶液中的慢一个数量级以上。ED对脂质头基团与疏水核心之间的膜界面具有高亲和力。ED的运动因其与膜脂的位点特异性强结合而减慢，并与膜脂基质同步。在足够大的脂质双分子层囊泡中，ED和脂质运动的减慢趋于平稳，尽管流体动力学连续体模型给出了与球形大小相反的脂质聚集运动减慢。有限运动与脂质双层膜的聚集体内流动性有关，膜不是刚性的，而是柔软的，波动的受限几何形状。该方法为深入了解这种受限但流体完整的细胞膜内的大范围分子动力学提供了可能性；既不需要标记也不需要侵入性探查。

Transport process of endocrine disruptors (ED) solubilized in phospholipid bilayer membranes was analyzed for the first time by NMR. The self-diffusion rates of ED, bisphenol A (BPA) and 4-octylphenol (OP), were directly determined and compared with those in water. Dynamics of the lipid matrices in membranes was simultaneously monitored without labeled nuclei. It owes its success to a specially designed high-power, high-sensitivity probe. The new probe can apply a large magnetic field-gradient sufficiently enough to monitor dynamic events in highly-viscous lipid membranes. Combining this probe to a high-resolution 600 MHz NMR apparatus, we showed how fast BPA, OP, and lipids moved in membrane and how the ED mobility was related to the membrane lipid dynamics. Attention was also paid to the relation of the ED mobility to the location in membrane.The ED transport in membrane was not rapid but more than one order of magnitude as slow as that in solution. ED had a high affinity for the membrane interface between the lipid headgroup and the hydrophobic core. The ED motion was slowed down by the site-specific, strong binding to membrane lipids and synchronized with that of the membrane lipid matrices.The slowdown of ED and lipid motions was leveled off in sufficiently large lipid bilayer vesicles, although the hydrodynamic continuum model gives the lipid aggregate motion slowed inversely to the spherical size. The limited motion is related to the intra-aggregate fluidity of the lipid bilayer membrane, the membrane not rigid but soft, fluctuating confined geometries. The method opens the possibility to give insight into the wide range of molecular dynamics within such confined but fluid intact cell membranes; neither labeling nor the invasive probing is required.