Chemical activity of cholesterol in membranes
Chemical activity of cholesterol in membranes
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DOI：
10.1021/bi0005097
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发表时间：
2000-07-18
期刊：
影响因子：
2.9
通讯作者：
McConnell, HM
中科院分区：
文献类型：
--
作者：
Radhakrishnan, A;McConnell, HM
本文报道了在空气-水界面恒定压力下，从均匀单层磷脂混合物中释放胆固醇（和二氢胆固醇）到β -环糊精的宿命常数的测量。在每一种混合物中，我们发现，通过与胆固醇-磷脂复合物的化学计量相对应的组成物，随着单层中胆固醇浓度的降低，释放率急剧下降。该配合物的化学计量学先前是通过每种混合物的热力学相图中的尖峰位置以及相对于组成测量的最小平均分子面积来确定的。先前用于解释相图的理论模型预测了这些混合物中胆固醇的化学势和化学活性。计算的化学活性也显示出均匀单层中复杂化学计量的急剧变化。观察到的释放速率和计算的化学活性变化的相似性是根据反应速率理论得出的，其中释放速率与胆固醇的化学活性成正比。胆固醇的化学活性由细胞质膜中某些磷脂和胆固醇之间的复合物形成决定，可能对细胞内胆固醇运输和生物合成起调节作用。
Measurements are reported for the fate constants for the release of cholesterol (and dihydrocholesterol) to beta-cyclodextrin from mixtures with phospholipids in homogeneous monolayers at constant pressure at the air-water interface. In each mixture, it is found that the release rate shows a sharp decrease as the cholesterol concentration in the monolayer decreases through a composition corresponding to the stoichiometry of a cholesterol-phospholipid complex. The stoichiometry of the complex was established previously by the position of a sharp cusp in the thermodynamic phase diagram of each mixture and also by a minimum in average molecular area versus composition measurements. A theoretical model used earlier to account for the phase diagrams predicts the chemical potential and chemical activity of cholesterol in these mixtures. The calculated chemical activity also shows a sharp change at the complex stoichiometry in homogeneous monolayers. The similarities in change of observed release rate and calculated chemical activity are expected from reaction rate theory where the release rate is proportional to the cholesterol chemical activity. The chemical activity of cholesterol as determined by complex formation between some phospholipids and cholesterol in the plasma membrane of cells may serve a regulatory function with respect to intracellular cholesterol transport and biosynthesis.