Heimburg T
Max-Planck Institut für biophysikalische Chemie, 37070 Göttingen, Germany.
Biophys J. 2000 Mar;78(3):1154-65. doi: 10.1016/S0006-3495(00)76673-2.
Below the thermotropic chain-melting transition, lipid membrane c(P) traces display a transition of low enthalpy called the lipid pretransition. It is linked to the formation of periodic membrane ripples. In the literature, these two transitions are usually regarded as independent events. Here, we present a model that is based on the assumption that both pretransition and main transition are caused by the same physical effect, namely chain melting. The splitting of the melting process into two peaks is found to be a consequence of the coupling of structural changes and chain-melting events. On the basis of this concept, we performed Monte Carlo simulations using two coupled monolayer lattices. In this calculation, ripples are considered to be one-dimensional defects of fluid lipid molecules. Because lipids change their area by approximately 24% upon melting, line defects are the only ones that are topologically possible in a triangular lattice. The formation of a fluid line defect on one monolayer leads to a local bending of the membrane. Geometric constraints result in the formation of periodic patterns of gel and fluid domains. This model, for the first time, is able to predict heat capacity profiles, which are comparable to the experimental c(P) traces that we obtained using calorimetry. The basic assumptions are in agreement with a large number of experimental observations.
在热致链熔化转变温度以下，脂质膜的c(P)曲线显示出一个低焓转变，称为脂质预转变。它与周期性膜波纹的形成有关。在文献中，这两个转变通常被视为独立事件。在此，我们提出一个模型，该模型基于这样的假设：预转变和主转变都是由相同的物理效应，即链熔化引起的。发现熔化过程分裂为两个峰是结构变化与链熔化事件耦合的结果。基于这一概念，我们使用两个耦合的单层晶格进行了蒙特卡罗模拟。在该计算中，波纹被视为流体脂质分子的一维缺陷。由于脂质在熔化时其面积大约变化24%，线缺陷是三角晶格中唯一拓扑上可能的缺陷。一个单层上流体线缺陷的形成会导致膜的局部弯曲。几何约束导致凝胶域和流体域的周期性图案形成。该模型首次能够预测热容量曲线，其与我们使用量热法获得的实验c(P)曲线相当。基本假设与大量实验观察结果一致。
