Putzel G Garbès, Schick M
Department of Physics, University of Washington, Seattle, Washington, USA.
Biophys J. 2008 Nov 15;95(10):4756-62. doi: 10.1529/biophysj.108.136317. Epub 2008 Aug 15.
We present a phenomenological theory for the phase behavior of ternary mixtures of cholesterol and saturated and unsaturated lipids, one that describes both liquid and gel phases. It leads to the following description of the mechanism of the phase behavior: In a binary system of the lipids, phase separation occurs when the saturated chains are well ordered, as in the gel phase, simply due to packing effects. In the liquid phase, the saturated ones are not sufficiently well ordered for separation to occur. The addition of cholesterol, however, increases the saturated lipid order to the point that phase separation is once again favorable. Our theory addresses this last mechanism-the means by which cholesterol-mediated ordering of membrane lipids leads to liquid-liquid immiscibility. It produces, for the system above the main chain transition of the saturated lipid, phase diagrams in which there can be liquid-liquid phase separation in the ternary system but not in any of the binary ones, while below that temperature it yields the more common phase diagram in which a gel phase, rich in saturated lipid, appears in addition to the two liquid phases.
我们提出了一种关于胆固醇与饱和及不饱和脂质三元混合物相行为的唯象理论，该理论描述了液相和凝胶相。它得出了以下关于相行为机制的描述：在脂质的二元体系中，当饱和链排列有序时，如在凝胶相中，仅仅由于堆积效应就会发生相分离。在液相中，饱和链的排列不够有序，不足以发生分离。然而，胆固醇的加入会增加饱和脂质的有序度，使得相分离再次变得有利。我们的理论探讨了这最后一种机制——胆固醇介导的膜脂质有序化导致液-液不混溶的方式。对于高于饱和脂质主链转变温度的体系，它给出的相图显示，三元体系中会出现液-液相分离，而二元体系中则不会；而在该温度以下，它给出的是更常见的相图，除了两个液相外，还会出现富含饱和脂质的凝胶相。
