Berkovich Anna K, Lukashev Eugeny P, Melik-Nubarov Nickolay S
M.V. Lomonosov Moscow State University, Russian Federation.
Biochim Biophys Acta. 2012 Mar;1818(3):375-83. doi: 10.1016/j.bbamem.2011.06.006. Epub 2011 Jun 16.
In this work, we report on the interaction of polyacrylic acid with phosphatidylcholine bilayers and monolayers in slightly acidic medium. We found that adsorption of polyacrylic acid on liposomes composed of egg lecithin at pH 4.2 results in the formation of small pores permeable for low molecular weight solutes. However, the pores were impermeable for trypsin indicating that no solubilization of liposomes occurred. The pores were permeable for both positively charged trypsin substrate N-benzoyl-l-arginine ethyl ester and negatively charged pH-indicator pyranine. Two lines of evidence were obtained confirming the involvement of the membrane dipole potential in the insertion of polyacrylic acid into lipid bilayer. (i) Addition of phloretin, a molecule which is known to decrease dipole potential of lipid bilayer, reduced the rate of a polyacrylic acid induced leakage of pyranine from liposomes. (ii) Direct measurements of air/lipid monolayer/water interface surface potential using Kelvin probe showed that adsorption of polyacrylic acid at pH 4.2 induced a decrease in both boundary and dipole potential by 37 and 62mV for ester lipid dioleoylphosphatidylcholine (DOPC). Replacement of DOPC by ether lipid 1,2-di-O-oleyl-sn-glycero-3-phosphocholine (DiOOPC) which is known to form monolayers and bilayers with only minor dipole component of membrane potential showed that addition of PAA produced similar response in the boundary potential (by 50mV) but negligible response in dipole potential of monolayer. These observations agree with our assumption that dipole potential is an important driving force for the insertion of polyacids into biological membranes.
在本研究中，我们报道了在微酸性介质中聚丙烯酸与磷脂酰胆碱双层膜和单层膜的相互作用。我们发现，在pH 4.2时，聚丙烯酸吸附在由卵磷脂组成的脂质体上会导致形成对低分子量溶质可渗透的小孔。然而，这些小孔对胰蛋白酶是不可渗透的，这表明脂质体没有发生溶解。这些小孔对带正电荷的胰蛋白酶底物N-苯甲酰-L-精氨酸乙酯和带负电荷的pH指示剂吡喃黄都是可渗透的。我们获得了两条证据，证实了膜偶极电势在聚丙烯酸插入脂质双层过程中的作用。（i）添加根皮素，一种已知会降低脂质双层偶极电势的分子，降低了聚丙烯酸诱导的吡喃黄从脂质体泄漏的速率。（ii）使用开尔文探针直接测量空气/脂质单层膜/水界面的表面电势，结果表明，在pH 4.2时，聚丙烯酸的吸附使酯脂质二油酰磷脂酰胆碱（DOPC）的边界电势和偶极电势分别降低了37mV和62mV。用醚脂质1,2-二油酰基-sn-甘油-3-磷酸胆碱（DiOOPC）取代DOPC，已知DiOOPC形成的单层膜和双层膜的膜电势偶极成分较小，结果表明，添加聚丙烯酸在边界电势上产生了类似的响应（降低了50mV），但在单层膜的偶极电势上产生的响应可忽略不计。这些观察结果与我们的假设一致，即偶极电势是多聚酸插入生物膜的重要驱动力。
