DETECTION OF CRYSTALLINE CHOLESTEROL MONOHYDRATE IN MODEL BIOMEMBRANES

生物膜中胆固醇的摩尔分数不同于 几乎为零到大约0.5。决定多少钱的原则 胆固醇可以在生物膜中调节目前还不是 明白了。一种热力学相对简单的现象 描述是胆固醇在双分子层中的最大溶解度， 超过这个范围，胆固醇就会以晶体的形式沉淀。我们能够 检测共存的微量胆固醇一水晶体 有磷脂-胆固醇片层。这种灵敏的侦测 使我们能够建立相边界以显示 晶相。国际象棋的x射线源提供了解决方案。 需要从低角度区分更高阶层状重复序列 一水合胆固醇线。胆固醇溶解度在人体内的价值 (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中， 值为0.50。造成这种差异的潜在分子基础是 不了解，但似乎涉及到集团领域。然而，a 简单的预测是，细胞内的血浆小叶 膜上的胆固醇含量应该比外叶少， 因为PE在内部传单中几乎是独家的位置。

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.