大分子拥挤环境中脂肪酸影响磷脂囊泡相变的差示扫描量热研究

脂肪酸诱导的磷脂膜的热力学行为对于认识细胞内复杂的机制有着重要意义，而前人在研究脂肪酸与磷脂膜相互作用时大都在稀溶液中进行；拥挤环境下脂肪酸诱导磷脂膜的相变行为还未见报道。本文以二肉豆蔻酰磷脂酰胆碱(DMPC)构建囊泡模型，采用差示扫描量热法系统地研究了在不同浓度、不同分子量的聚乙二醇(PEG)拥挤环境中不同结构的脂肪酸对DMPC磷脂囊泡相变的影响。研究结果表明，在拥挤环境中，PEG对纯的磷脂囊泡相变的影响与大分子的分子量和浓度相关。对于脂肪酸/磷脂囊泡(FA/DMPC)，PEG的存在对囊泡相变产生显著影响。在所考察的分子量和浓度范围内，PEG使FA/DMPC囊泡相变增加。短链饱和脂肪酸、不饱和脂肪酸原本使DPMC囊泡相变降低，但PEG缩小了降低幅度，甚至导致相变增加。进一步的研究表明，在大多数情况下，PEG对FA/DMPC的相变具有协作增强效应，且其影响均与大分子的分子量和浓度相关。另外，随着PEG浓度的升高，磷脂囊泡的协同单位数逐渐降低，表明拥挤环境会影响磷脂双分子层的均一性，使协同发生相变的分子数降低。本文的研究表明，大分子拥挤环境能够对扰动的磷脂双分子层起到一定的修复作用，这一现象在生物膜相关领域不可忽视。

Phase Transition of Phospholipid Vesicles Induced by Fatty Acids in Macromolecular Crowding: a Differential Scanning Calorimetry Study

Investigation of the thermodynamics of fatty acid (FA) modulation of lipid membrane behavior is important to understand the mechanisms that occur in cells. Previous research of the interaction between FAs and lipid membranes has been performed in dilute solution, and no study has focused on the effect of an external crowding medium on the phase transition of the lipid membrane induced by FAs. In this paper, the effect of various molecular weights and concentrations of polyethylene glycol (PEG) on the phase transition of 1, 2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) vesicles mixed with FA was systematically investigated by differential scanning calorimetry (DSC). The results show that the effect of PEG on the phase transition of pure DMPC vesicles is both molecular weight and concentration dependent. The presence of PEG significantly changes the phase transition of FA/DMPC vesicles. Phase transition temperature (T_m) of FA/DMPC vesicles increased in PEG for most of the considered concentrations and molecular weights. The original T_m of DMPC induced by short-chain saturated FA or unsaturated FA increased in the presence of PEG. Further investigation revealed that in most cases a collaborative effect of molecular crowding existed and the effect of PEG on T_m was both molecular weight and concentration dependent. Moreover, the cooperative unit (CU) of pure DMPC vesicles and most FA/DMPC systems decreased with increasing PEG concentration, indicating that the crowded medium contributes to the heterogeneity of the bilayers and that fewer molecules cooperatively participate in the phase transition. The results suggest that crowded media might repair disturbed membranes, which should not be ignored in the FA-modulating membrane related area.