EPR LINEWIDTH (T2) METHOD TO MEASURE MEMBRANE OXYGEN PERMEABILITY

众所周知，氮氧化物的连续波EPR谱 引入磷脂双层的探针(标记)对 分子氧。然而，氧气的准确测定 这些实验的展宽因形状复杂而变得复杂 受各向异性强烈影响的EPR谱 限制了探针分子的运动。一种准确的方法是 提出了从测量的光谱中提取氧气展宽的方法 在相同的温度下，在有氧和无氧条件下。方法是 基于Levenberg-MarQuardt的快速卷积算法 优化。该方法以前应用于EPR血氧测定仪 在快速极限下表现出旋转运动的氮氧化物。它是 结果表明，对于几种膜自旋探针，氧增宽可以 被描述为均匀的；因此，单线宽参数拟合 模型是合适的。将该方法应用于渗透率的测量 1，2-二肉豆蔻基锡-甘油模型膜的研究 -3-磷胆碱在主相变上、下。对两个人都是 膜相，羟基型和甾醇型标记的加宽是 发现是同质的，这一发现与 分子氧和自旋探针之间的海森堡交换。作为一种 应用该方法研究了乙醇对局部环境的影响。 磷脂双层膜的透氧性。结果表明， 低至1%(v/v)的乙醇浓度可提高透氧率 双层的。膜表面的影响较大。 表明乙醇分子相互作用 主要在双层的极头区域内。这是一个 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.