The behavior of dioleoylphosphatidylethanolamine (DOPE)/cholesterol/tetradecane and dioleoylphosphatidylcholine (DOPC)/cholesterol/tetradecane were examined using x-ray diffraction and the osmotic stress method. DOPE/tetradecane, with or without cholesterol, forms inverted hexagonal (HII) phases in excess water. DOPC/tetradecane forms lamellar phases without cholesterol at lower temperatures. With tetradecane, as little as 5 mol% cholesterol in DOPC induced the formation of HII phases of very large dimension. Increasing levels of cholesterol result in a systematic decrease in the HII lattice dimension for both DOPE and DOPC in excess water. Using osmotic pressure to control hydration, we applied a recent prescription to estimate the intrinsic curvature and bending modulus of the HII monolayers. The radii of the intrinsic curvature, RPO, at a pivotal plane of constant area within the monolayer were determined to be 29.4 A for DOPE/tetradecane at 22 degrees C, decreasing to 27 A at 30 mol% cholesterol. For DOPC/tetradecane at 32 degrees C, RPO decreased from 62.5 A to 40 A as its cholesterol content increased from 30 to 50 mol%. These data yielded an estimate of the intrinsic radius of curvature for pure DOPC of 87.3 A. The bending moduli kc of DOPE/tetradecane and DOPC/tetradecane, each with 30 mol% cholesterol, are 15 and 9 kT, respectively. Tetradecane itself was shown to have little effect on the bending modulus in the cases of DOPE and cholesterol/DOPE. Surprisingly, cholesterol effected only a modest increase in the kc of these monolayers, which is much smaller than estimated from its effect on the area compressibility modulus in bilayers. We discuss possible reasons for this difference.

译文

使用x射线衍射和渗透应力方法检查了二油基磷脂酰乙醇胺 (DOPE)/胆固醇/十四烷和二油基磷脂酰胆碱 (DOPC)/胆固醇/十四烷的行为。含或不含胆固醇的涂料/十四烷在过量的水中形成倒置的六边形 (HII) 相。DOPC/十四烷在较低温度下形成无胆固醇的层状相。使用十四烷时,DOPC中只有5 mol % 的胆固醇会诱导形成非常大尺寸的HII相。胆固醇水平的增加导致过量水中DOPE和DOPC的HII晶格尺寸系统性降低。使用渗透压控制水合作用,我们应用了最近的处方来估算HII单层的固有曲率和弯曲模量。在单层内恒定面积的枢转平面上的本征曲率半径RPO被确定为在22 ℃ 下的涂料/十四烷的29.4 a,在30摩尔 % 胆固醇下降至27 A。对于32 ℃ 的DOPC/十四烷,随着其胆固醇含量从30摩尔 % 增加到50摩尔 %,RPO从62.5 A降低到40 A。这些数据产生了87.3 A的纯DOPC的固有曲率半径的估计。胆固醇含量为30 mol % 的DOPE/十四烷和DOPC/十四烷的弯曲模量kc分别为15和9 kT。在涂料和胆固醇/涂料的情况下,十四烷本身对弯曲模量的影响很小。令人惊讶的是,胆固醇仅影响了这些单层的kc的适度增加,这比根据其对双层中的面积可压缩模量的影响所估计的要小得多。我们讨论这种差异的可能原因。

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