Lipid bilayers form the basis of cell membranes and the phase behaviour of the membrane has been linked to proper cell function. Model membranes composed of relatively simple mixtures of phospholipids and cholesterol can already exhibit complex phase behaviour. Specifically, liquid ordered-liquid disordered fluid phase coexistence occurs in mixtures which contain one saturated long chain phospholipid and one unsaturated long chain phospholipid and cholesterol. This fluid-fluid two phase region persists over a broad range of temperatures and sample compositions and can be observed experimentally in various sample preparations including multilamellar dispersions, bicelles, and multi-lamellae stacked on glass slides. In order to explore the practicality of using oriented samples with different concentrations of the peptide, we investigated the effect of the addition of a synthetic 22 residue amphiphilic peptide on the orientability and phase behaviour of the lipid mixtures, as well as the orientation and dynamics of the peptide itself via 2H NMR. Increasing the peptide concentration promoted the formation of the liquid ordered phase, suggesting a preferential interaction of the peptide with the thicker ordered phase. However, higher peptide content (> 4 mol%) had a significant negative effect on the alignment of bicelles with their bilayer normal perpendicular to the external magnetic field. In the stacked bilayer samples, 6 mol% peptide eliminated the two phase coexistence region altogether and a single liquid ordered phase was observed from 285 to 311 K. Even so, 2H spectra of the peptide itself did not reveal any preference for the peptide to partition into either the liquid disordered or liquid ordered phase and we found two populations of the peptide, one which undergoes rapid axial reorientation about the bilayer normal and a second (powder component) which does not.

中文翻译：

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含有两亲肽的定向磷脂/胆固醇双层的2 H NMR。

脂质双层形成细胞膜的基础，膜的相行为已与适当的细胞功能有关。由相对简单的磷脂和胆固醇混合物组成的模型膜已经表现出复杂的相行为。具体地说，在含有一种饱和长链磷脂和一种不饱和长链磷脂与胆固醇的混合物中，发生有序有序无序液相。该流体-流体两相区域可在很宽的温度和样品组成范围内持续存在，并且可以在各种样品制备中通过实验观察到，这些样品制备包括多层分散体，双室和堆叠在载玻片上的多层。为了探索使用具有不同浓度肽段的定向样品的实用性，我们研究了添加合成的22个残基的两亲性肽对脂质混合物的定向性和相行为的影响，以及通过2H NMR对肽本身的定向和动力学的影响。肽浓度的增加促进了液相有序相的形成，表明肽与较厚的有序相的优先相互作用。但是，较高的肽含量（> 4 mol％）对Bicells的双层法线垂直于外部磁场的排列具有明显的负面影响。在堆叠的双层样品中，6 mol％的肽完全消除了两相共存区域，并且在285至311 K范围内观察到了单个液相有序相。