DETECTION OF CRYSTALLINE CHOLESTEROL MONOHYDRATE IN MODEL BIOMEMBRANES

生物膜中胆固醇的摩尔分数从 接近零到约0.5。 这些原则决定了 胆固醇可以容纳在生物膜中， 明白 一个相对简单的热力学现象 描述了胆固醇在双层中的最大溶解度， 超过此胆固醇沉淀为晶体。 我们能够 检测共存的痕量胆固醇一水合物晶体 磷脂-胆固醇脂质体。 这种灵敏的检测 使我们能够建立相边界的外观， 结晶相 CHESS的X射线源提供了分辨率 需要区分高阶层状重复与低角度 胆固醇一水合物线。 胆固醇溶解度值 (16：0，18：19）-PC，（12：0，12：0）-PC，（22：113，22：113）-PC，和 (16：0，18：19）-PS为摩尔分数0.66。 在（16：0，18：19）-PE， 值为0.50。 这种差异的潜在分子基础是 不明白，但似乎涉及头群区。 但 简单的预测是，细胞浆的内部小叶 膜应该比外小叶含有更少的胆固醇， 因为PE几乎完全位于内瓣叶中。

The mole fraction of cholesterol in biomembranes varies from nearly zero to about 0.5. The principles that determine how much cholesterol can be accomodated in a biomembrane are not yet understood. A phenomenon with a relatively simple thermodynamic description is the maximum solubility of cholesterol in a bilayer, beyond which cholesterol precipitates as crystals. We were able to detect trace amounts of cholesterol monohydrate crystals coexisting with phospholipid-cholesterol lamellae. This sensitive detection enabled us to establish the phase boundary for appearance of the crystalline phase. The x-ray source at CHESS provided the resolution needed to distinguish higher order lamellar repeats from the low angle cholesterol monohydrate lines. The value of cholesterol solubility in (16:0,18:19)-PC, (12:0,12:0)-PC, (22:113,22:113)-PC, and (16:0,18:19)-PS is mole fraction 0.66. In (16:0,18:19)-PE, the value is 0.50. The underlying molecular basis for this difference is not understood, but seems to involve headgroup area. However, a simple prediction is that the inner leaflet of cellular plasma membranes should contain less cholesterol than the outer leaflet, because of the nearly exclusive location of PE in the inner leaflet.