Goñi F M, Urbaneja M A, Arrondo J L, Alonso A, Durrani A A, Chapman D
Eur J Biochem. 1986 Nov 3;160(3):659-65. doi: 10.1111/j.1432-1033.1986.tb10088.x.
The interaction of multilamellar phosphatidylcholine vesicles with the non-ionic detergent Triton X-100 has been studied under equilibrium conditions, specially in the sub-lytic range of surfactant concentrations. Equilibrium was achieved in less than 24 h. Estimations of detergent binding to bilayers, using [3H]Triton X-100, indicate that the amphiphile is incorporated even at very low concentrations (below its critical micellar concentration); a dramatic increase in the amount of bound Triton X-100 occurs at detergent concentrations just below those producing membrane solubilization. Solubilization occurs at phospholipid/detergent molar ratios near 0.65 irrespective of lipid concentration. The perturbation produced by the surfactant in the phospholipid bilayer has been studied by differential scanning calorimetry, NMR and Fourier-transform infrared spectroscopy. At low detergent concentration (lipid/detergent molar ratios above 3), a reduction in 2H-NMR quadrupolar splitting occurs, suggesting a decrease in the static order of the acyl chains; the same effect is detected by Fourier-transform infrared spectroscopy in the form of blue shifts of the methylene stretching vibration bands. Simultaneously, the enthalpy variation of the main phospholipid phase transition is decreased by about a third with respect to its value in the pure lipid/water system. For phospholipid/detergent molar ratios between 3 and 1, the decrease in lipid static order does not proceed any further; rather an increase in fluidity is observed, characterized by a marked decrease in the midpoint transition temperature of the gel-to-fluid phospholipid transition. At the same time an isotropic component is apparent in both 31P-NMR and 2H-NMR spectra, and a new low-temperature endotherm is detected in differential scanning calorimetric traces. When phospholipid and Triton X-100 are present at equimolar ratios some bilayer structure persists, as judged from calorimetric observations, but NMR reveals only one-component isotropic signals. At lipid/detergent molar ratios below unity, the NMR lines become narrower, the main (lamellar) calorimetric endotherm tends to vanish and solubilization occurs.
在平衡条件下，特别是在表面活性剂浓度的亚裂解范围内，研究了多层磷脂酰胆碱囊泡与非离子洗涤剂Triton X-100的相互作用。在不到24小时内达到平衡。使用[3H]Triton X-100对洗涤剂与双层膜的结合进行估计，结果表明即使在非常低的浓度（低于其临界胶束浓度）下，两亲分子也会掺入；在刚好低于产生膜溶解的洗涤剂浓度时，结合的Triton X-100量会急剧增加。无论脂质浓度如何，在磷脂/洗涤剂摩尔比接近0.65时都会发生溶解。通过差示扫描量热法、核磁共振和傅里叶变换红外光谱研究了表面活性剂对磷脂双层的扰动。在低洗涤剂浓度下（脂质/洗涤剂摩尔比高于3），2H-核磁共振四极分裂减小，表明酰基链的静态有序度降低；傅里叶变换红外光谱以亚甲基伸缩振动带的蓝移形式检测到相同的效应。同时，相对于纯脂质/水体系中的值，主要磷脂相变的焓变降低了约三分之一。对于磷脂/洗涤剂摩尔比在3到1之间，脂质静态有序度的降低不再进一步进行；相反，观察到流动性增加，其特征是凝胶-流体磷脂转变的中点转变温度显著降低。同时，在31P-核磁共振和2H-核磁共振光谱中都出现了各向同性成分，并且在差示扫描量热曲线中检测到一个新的低温吸热峰。当磷脂和Triton X-100以等摩尔比存在时，从量热观察判断，一些双层结构仍然存在，但核磁共振仅显示单组分各向同性信号。在脂质/洗涤剂摩尔比低于1时，核磁共振谱线变窄，主要的（层状）量热吸热峰趋于消失并发生溶解。
