Ionescu Diana, Ganea Constanţa
University of Medicine and Pharmacy "Carol Davila", 050474, Bucharest, Romania,
Eur Biophys J. 2012 Feb 3. doi: 10.1007/s00249-011-0786-0.
Quercetin (QCT) is an important bioactive natural compound found in numerous edible plants. Since the lipid bilayer represents an essential compound of the cell membrane, QCT's direct interaction with this structure is of great interest. Therefore, we proposed to study the effects of QCT on DMPC liposomes containing cholesterol (Chol), and for this purpose Laurdan fluorescence was used. As a fluorescent probe, Laurdan is able to detect changes in membrane phase properties. When incorporated in lipid bilayers, Laurdan emits from two different excited states, a non-relaxed one when the bilayer packing is tight and a relaxed state when the bilayer packing is loose. The main tool for quantifying QCT's effects on phospholipid membranes containing Chol has been the analysis, the decomposition of Laurdan emission spectra in sums of two Gaussian functions on energy. This kind of approach has allowed good analysis of the balance between the two emitting states of Laurdan. Our results show that both Laurdan emission states are present to different extents in a wide temperature range for DMPC liposomes with Chol. QCT is decreasing the phase transition temperature in pure DMPC liposomes as proved by generalized polarization (GP) values. QCT also quenches Laurdan fluorescence, depending on the temperature and the presence of Chol in the membrane. Stern-Volmer constants were calculated for different lipid membrane compositions, and the conclusion was that the relaxed state favors the nonradiative transitions of the fluorophore.
槲皮素（QCT）是一种存在于多种可食用植物中的重要生物活性天然化合物。由于脂质双层是细胞膜的重要组成部分，QCT与该结构的直接相互作用备受关注。因此，我们提议研究QCT对含胆固醇（Chol）的二肉豆蔻酰磷脂酰胆碱（DMPC）脂质体的影响，并为此使用了劳丹荧光法。作为一种荧光探针，劳丹能够检测膜相性质的变化。当掺入脂质双层时，劳丹从两种不同的激发态发射，当双层堆积紧密时为非弛豫态，当双层堆积松散时为弛豫态。量化QCT对含Chol的磷脂膜影响的主要工具是分析，即将劳丹发射光谱分解为两个高斯函数能量之和。这种方法能够很好地分析劳丹两种发射态之间的平衡。我们的结果表明，对于含Chol的DMPC脂质体，在很宽的温度范围内，劳丹的两种发射态均不同程度地存在。广义极化（GP）值证明，QCT降低了纯DMPC脂质体的相变温度。QCT还会淬灭劳丹荧光，这取决于温度和膜中Chol的存在情况。计算了不同脂质膜组成的斯特恩-沃尔默常数，得出的结论是弛豫态有利于荧光团的非辐射跃迁。
