Fretten P, Morris S J, Watts A, Marsh D
Biochim Biophys Acta. 1980 May 23;598(2):247-59. doi: 10.1016/0005-2736(80)90003-6.
The ESR spectra of six different positional isomers of a stearic acid and three of a phosphatidylcholine spin label have been studied as a function of temperature in chromaffin granule membranes from the bovine adrenal medulla, and in bilayers formed by aqueous dispersion of the extracted membrane lipids. Only minor differences were found between the spectra of the membranes and the extracted lipid, indicating that the major portion of the membrane lipid is organized in a bilayer arrangement which is relatively unperturbed by the presence of the membrane protein. The order parameter profile of the spin label lipid chain motion is less steep over the first half of the chain than over the section toward the terminal methyl end of the chain. This 'stiffening' effect is attributed to the high proportion of cholesterol in the membrane and becomes less marked as the temperature is raised. The isotropic hyperfine splitting factors of the various positional isomers display a profile of decreasing polarity as one penetrates further into the interior of the membrane. No marked differences are observed between the effective polarities in the intact membranes and in bilayers of the extracted membrane lipids. The previously observed temperature-induced structural change occurring in the membranes at approx. 35 degrees C was found also in the extracted lipid bilayers, showing this to be a result of lipid-lipid interactions and not lipid-protein interactions in the membrane. A steroid spin label indicated a second temperature-dependent structural change occurring in the lipid bilayers at lower temperatures. This correspond to the onset of a more rapid rotation about the long axis of the lipid molecules at a temperature of approx. 10 degrees C. The lipid bilayer regions probed by the spin labels used in this study may be involved in the fusion of the chromaffin granule membrane leading to hormone release by exocytosis.
研究了硬脂酸六种不同位置异构体以及磷脂酰胆碱自旋标记物三种异构体的电子自旋共振（ESR）谱随温度的变化情况，研究对象为牛肾上腺髓质嗜铬颗粒膜以及由提取的膜脂水分散形成的双层膜。在膜和提取脂质的谱图之间仅发现了微小差异，这表明膜脂的主要部分以双层排列方式组织，且相对不受膜蛋白存在的干扰。自旋标记脂质链运动的序参数曲线在前半段链上比朝着链末端甲基端的部分更平缓。这种“硬化”效应归因于膜中胆固醇的高比例，并且随着温度升高而变得不那么明显。随着向膜内部深入，各种位置异构体的各向同性超精细分裂因子呈现出极性降低的分布。在完整膜和提取膜脂双层中的有效极性之间未观察到明显差异。先前观察到的膜在约35℃发生的温度诱导结构变化在提取的脂质双层中也被发现，这表明这是脂质 - 脂质相互作用而非膜中脂质 - 蛋白质相互作用的结果。一种类固醇自旋标记表明在较低温度下脂质双层中发生了第二种温度依赖性结构变化。这对应于在约10℃时脂质分子围绕长轴的旋转速度加快。本研究中使用的自旋标记所探测的脂质双层区域可能参与了嗜铬颗粒膜的融合，从而导致通过胞吐作用释放激素。
