Pabst Georg, Hodzic Aden, Strancar Janez, Danner Sabine, Rappolt Michael, Laggner Peter
Institute of Biophysics and Nanosystems Research, Austrian Academy of Sciences, Graz, Austria.
Biophys J. 2007 Oct 15;93(8):2688-96. doi: 10.1529/biophysj.107.112615. Epub 2007 Jun 22.
We studied the influence of sodium and calcium chloride on the global and local membrane properties of fluid palmitoyl-oleoyl phosphatidylcholine bilayers, applying synchrotron small-angle x-ray diffraction, spin-labeling electron paramagnetic resonance spectroscopy, and differential scanning calorimetry, as well as simultaneous density and acoustic measurements. The salt concentration was varied over a wide range from 0 to 5 M. We found that NaCl leads to a continuous swelling of the bilayers, whereas the behavior of the bilayer separation dW in the presence of CaCl2 is more complex, showing an initial large dW value, which decreased upon further addition of salt and finally increased again in the high concentration regime. This can be understood by a change of balance between electrostatic and van der Waals interactions. We were further able to show that both salts lead to a significant increase of order within the lipid bilayer, leading to a decrease of bilayer elasticity and shift of main phase transition temperature. This effect is more pronounced for Ca2+, and occurs mainly in the high salt-concentration regime. Thus, we were able to reconcile previous controversies between molecular dynamics simulations and x-ray diffraction experiments regarding the effect of salts on neutral lipid bilayers.
我们运用同步加速器小角X射线衍射、自旋标记电子顺磁共振波谱、差示扫描量热法以及同步密度和声测量，研究了氯化钠和氯化钙对液态棕榈酰油酰磷脂酰胆碱双层膜整体和局部膜性质的影响。盐浓度在0至5 M的宽范围内变化。我们发现，氯化钠会导致双层膜持续膨胀，而在氯化钙存在的情况下，双层膜间距dW的行为更为复杂，呈现出初始较大的dW值，在进一步添加盐时该值会减小，最终在高浓度区域又再次增大。这可以通过静电相互作用和范德华相互作用之间平衡的变化来理解。我们还能够表明，两种盐都会导致脂质双层内有序度显著增加，从而导致双层膜弹性降低和主相变温度偏移。这种效应对于Ca2+更为明显，且主要发生在高盐浓度区域。因此，我们能够调和先前分子动力学模拟和X射线衍射实验之间关于盐对中性脂质双层膜影响的争议。
