EPR linewidth (T2) method to measure oxygen permeability of phospholipid bilayers and its use to study the effect of low ethanol concentrations.
EPR linewidth (T2) method to measure oxygen permeability of phospholipid bilayers and its use to study the effect of low ethanol concentrations.
复制标题
EPR 线宽 (T2) 方法测量磷脂双层的氧渗透性及其用于研究低乙醇浓度的影响。
DOI：
10.1006/jmrb.1996.0073
复制
发表时间：
1996
期刊：
影响因子：
--
通讯作者：
R. Belford
中科院分区：
文献类型：
--
作者：
Alex I. Smirnov;R. Clarkson;R. Belford
众所周知，引入磷脂双层膜的氮氧化物探针(标记物)的连续波EPR谱对分子氧敏感。然而，由于EPR谱形状复杂，受探针分子各向异性限制运动的强烈影响，准确测定氧的展宽是复杂的。提出了一种从同一温度下测得的有氧和无氧的光谱中准确提取氧增宽的方法。该方法基于一种快速卷积算法，并结合了Levenberg-MarQuardt优化算法。这种方法以前被应用于氮氧化物在快速极限下表现出旋转运动的EPR血氧测定。结果表明，对于几种膜自旋探针，氧的展宽可以描述为均匀的，因此，直线宽度参数拟合模型是合适的。将该方法应用于由1，2-二肉豆蔻基-sn-甘油-3-磷胆碱组成的模型膜在主相变前后的渗透曲线的测量。对于两种膜相，都发现DOXY型和STO型标记物的加宽是均匀的，这一发现与分子氧和自旋探针之间的海森堡交换模型一致。作为例子，应用该方法研究了乙醇对磷脂双层膜局部透氧性的影响。结果表明，乙醇浓度低至1%(v/v)时，双层膜的透氧率增加。膜表面的影响大于膜中心的影响，这表明乙醇分子主要在双层的极性头部区域内相互作用。
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 ethanol 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.