EPR LINEWIDTH (T2) METHOD TO MEASURE MEMBRANE OXYGEN PERMEABILITY

氮氧化合物的连续EPR谱 引入磷脂双层的探针（标记）对 分子氧 然而，准确测定氧气 从这些实验中得到的加宽由于复杂的形状而变得复杂 的EPR谱，这是强烈的影响，各向异性 限制探针分子的运动。 准确的方法是 提出从测量的光谱中提取氧增宽 在相同的温度下，有氧和无氧的情况下。 该方法 基于Levenberg-Marquardt快速卷积算法 优化. 该方法先前应用于EPR血氧测定， 在快极限下表现出旋转运动的氮氧化合物。 是 表明对于几种膜自旋探针，氧增宽可以 被描述为均匀的;因此，一个线宽参数拟合 模型是合适的。 将该方法应用于渗透率的测量 由1，2-二肉豆蔻酰-sn-甘油组成的模型膜的分布 -3-磷酸胆碱的上方和下方的主要相变。 为 膜相，doxyl和甾醇型标记的增宽是 发现是同质的，这一发现与 分子氧与自旋探针之间的海森堡交换。 作为 实例分析表明，该方法可用于研究乙醇对局部 磷脂双层的透氧性。 它示出 乙醇浓度低至1%（v/v）时， 双层的。 在膜的表面， 表明乙醇分子之间的相互作用 主要在双层的极性头部区域内。 这是一 正在进行的多年项目。

It is well known that continuous-wave EPR spectra of nitroxide probes (labels) introduced into phospholipid bilayers are sensitive to molecular oxygen. However, accurate determination of oxygen broadening from these experiments is complicated by the complex shapes of EPR spectra, which are strongly influenced by anisotropic restricted motion of the probe molecules. An accurate method is presented to extract the oxygen broadening from the spectra measured with and without oxygen and at the same temperature. The method is based on a fast convolution algorithm with Levenberg-Marquardt optimization. This method was previously applied to EPR oximetry with nitroxides exhibiting rotational motion in the fast limit. It is shown that for several membrane spin probes, the oxygen broadening can be described as homogeneous; thus, a one-linewidth-parameter fitting model is appropriate. The method is applied to measure permeability profiles of model membranes composed from 1,2-dimyristoyl-sn-glycero -3-phosphocholine above and below the main phase transition. For both membrane phases, the broadening of doxyl- and sterol-type labels is found to be homogeneous, a finding consistent with the model of Heisenberg exchange between molecular oxygen and spin probes. As an example, the method is applied to study the ethanol effect on local oxygen permeability of a phospholipid bilayer. It is shown that ehanol concentrations as low as 1% (v/v) increase oxygen permeability of the bilayer. The effect is larger at the surface of the membrane than at its center, indicating that ethanol molecules interact primarily within the polar head region of the bilayer. This is an ongoing multi-year project.