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首页> 美国卫生研究院文献>Biophysical Journal >Differential scanning calorimetric and Fourier transform infrared spectroscopic studies of the effects of cholesterol on the thermotropic phase behavior and organization of a homologous series of linear saturated phosphatidylserine bilayer membranes.
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Differential scanning calorimetric and Fourier transform infrared spectroscopic studies of the effects of cholesterol on the thermotropic phase behavior and organization of a homologous series of linear saturated phosphatidylserine bilayer membranes.

机译：差示扫描量热法和傅里叶变换红外光谱研究胆固醇对热致变相行为和线性饱和磷脂酰丝氨酸双层膜同源系列的组织的影响。

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We have examined the effects of cholesterol on the thermotropic phase behavior and organization of aqueous dispersions of a homologous series of linear disaturated phosphatidylserines by high-sensitivity differential scanning calorimetry and Fourier transform infrared spectroscopy. We find that the incorporation of increasing quantities of cholesterol progressively reduces the temperature, enthalpy, and cooperativity of the gel-to-liquid-crystalline phase transition of the host phosphatidylserine bilayer, such that a cooperative chain-melting phase transition is completely or almost completely abolished at 50 mol % cholesterol, in contrast to the results of previous studies. We are also unable to detect the presence of a separate anhydrous cholesterol or cholesterol monohydrate phase in our binary mixtures, again in contrast to previous reports. We further show that the magnitude of the reduction in the phase transition temperature induced by cholesterol addition is independent of the hydrocarbon chain length of the phosphatidylserine studied. This result contrasts with our previous results with phosphatidylcholine bilayers, where we found that cholesterol increases or decreases the phase transition temperature in a chain length-dependent manner (1993. Biochemistry, 32:516-522), but is in agreement with our previous results for phosphatidylethanolamine bilayers, where no hydrocarbon chain length-dependent effects were observed (1999. Biochim. Biophys. Acta, 1416:119-234). However, the reduction in the phase transition temperature by cholesterol is of greater magnitude in phosphatidylethanolamine as compared to phosphatidylserine bilayers. We also show that the addition of cholesterol facilitates the formation of the lamellar crystalline phase in phosphatidylserine bilayers, as it does in phosphatidylethanolamine bilayers, whereas the formation of such phases in phosphatidylcholine bilayers is inhibited by the presence of cholesterol. We ascribe the limited miscibility of cholesterol in phosphatidylserine bilayers reported previously to a fractional crystallization of the cholesterol and phospholipid phases during the removal of organic solvent from the binary mixture before the hydration of the sample. In general, the results of our studies to date indicate that the magnitude of the effect of cholesterol on the thermotropic phase behavior of the host phospholipid bilayer, and its miscibility in phospholipid dispersions generally, depend on the strength of the attractive interactions between the polar headgroups and the hydrocarbon chains of the phospholipid molecule, and not on the charge of the polar headgroups per se.
机译：我们已经通过高敏度差示扫描量热法和傅里叶变换红外光谱法研究了胆固醇对一系列线性不饱和磷脂酰丝氨酸同源系列的热致变相行为和水分散体组织的影响。我们发现，越来越多的胆固醇的掺入逐渐降低了主体磷脂酰丝氨酸双层的凝胶-液晶相变的温度，焓和协同作用，从而使协同链熔化相变完全或几乎完全消失。与以前的研究结果相反，在50摩尔％的胆固醇水平下废除了。同样，我们也无法检测到我们的二元混合物中存在单独的无水胆固醇或胆固醇一水合物相，这与之前的报道再次相反。我们进一步表明，由胆固醇添加引起的相变温度降低的幅度与所研究的磷脂酰丝氨酸的烃链长度无关。该结果与我们先前关于磷脂酰胆碱双层的结果相反，我们发现胆固醇以链长依赖性方式增加或降低相变温度（1993. Biochemistry，32：516-522），但与我们先前的结果一致对于磷脂酰乙醇胺双层膜，没有观察到烃链长度依赖性效应（1999.Biochim.Biophys.Acta，1416：119-234）。然而，与磷脂酰丝氨酸双层相比，磷脂酰乙醇胺中胆固醇引起的相变温度降低幅度更大。我们还表明，胆固醇的添加促进了磷脂酰丝氨酸双层中层状结晶相的形成，就像磷脂酰乙醇胺双层中那样，而胆固醇的存在则抑制了磷脂酰胆碱双层中此类相的形成。我们将先前报道的磷脂在磷脂酰丝氨酸双层中有限的混溶性归因于在样品水合之前从二元混合物中去除有机溶剂期间胆固醇和磷脂相的部分结晶。通常，迄今为止我们的研究结果表明，胆固醇对主体磷脂双层的热致相行为的影响程度及其在磷脂分散液中的可混溶性通常取决于极性头基之间的吸引力相互作用的强度。和磷脂分子的烃链，而不是极性头基本身的电荷。

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