Jacobsohn M K, Bazilian L S, Hardiman J, Jacobsohn G M
Department of Biological Chemistry, Hahnemann University, Philadelphia, PA 19102.
Lipids. 1989 May;24(5):375-82. doi: 10.1007/BF02535144.
The ability of multilamellar vesicles of phosphatidylcholine and phosphatidylethanolamine in aqueous phase to prevent access to cholesterol by a nonpolar solvent was examined. Phosphatidylethanolamine vesicles. In mixed vesicles, cholesterol was retained in proportion to the amount of phosphatidylcholine. To alter the charge and hydration of head groups, pH was adjusted from 1.2 to 12.5. Above pH 8, both phosphatidylethanolamine and phosphatidylcholine retained sterol in a 1:1 molar ratio of phospholipid to cholesterol, regardless of acyl side chain composition. Between pH 2.0 and pH 8.0, sterol retention varied with type of head group and side chain. Lipids with 16-carbon saturated side chains retained more sterol than 18-carbon unsaturated or 12-carbon saturated side chains. Between pH 1.1 and 2.0, none of the phosphatidylethanolamines retained sterol, but long chain phosphatidylcholines, saturated or unsaturated, retained sterol in a 1:1 molar ratio of phospholipid to sterol. Short chain phosphatidylethanolamines and phosphatidylcholines retained 0 to 20% at the low- to mid-pH range. Size of multilamellar vesicles, measured by Doppler effect light scattering analysis, had no bearing on sterol retention. Sonication of vesicles, which increases surface curvature, increases the retention of sterol. Fluorescence polarization indicated that cholesterol does not interact with DPPC or DLPC side chains. The observations can be interpreted in terms of space requirements of head groups, including charge repulsion and hydration. Other factors, such as monovalent cation replacement by protons, juxtaposition of charged groups on vesicle surfaces and length and unsaturation of acyl side chains affect the affinity of phospholipids for cholesterol.
研究了水相中磷脂酰胆碱和磷脂酰乙醇胺的多层囊泡阻止非极性溶剂接触胆固醇的能力。磷脂酰乙醇胺囊泡。在混合囊泡中，胆固醇的保留量与磷脂酰胆碱的量成比例。为了改变头部基团的电荷和水合作用，将pH从1.2调节到12.5。在pH 8以上，无论酰基侧链组成如何，磷脂酰乙醇胺和磷脂酰胆碱都以磷脂与胆固醇1:1的摩尔比保留甾醇。在pH 2.0至pH 8.0之间，甾醇保留量随头部基团类型和侧链而变化。具有16碳饱和侧链的脂质比18碳不饱和或12碳饱和侧链保留更多的甾醇。在pH 1.1至2.0之间，没有一种磷脂酰乙醇胺保留甾醇，但长链磷脂酰胆碱，无论是饱和的还是不饱和的，都以磷脂与甾醇1:1的摩尔比保留甾醇。短链磷脂酰乙醇胺和磷脂酰胆碱在低至中pH范围内保留0至20%。通过多普勒效应光散射分析测量的多层囊泡大小与甾醇保留无关。囊泡的超声处理增加了表面曲率，增加了甾醇的保留。荧光偏振表明胆固醇不与二棕榈酰磷脂酰胆碱（DPPC）或二月桂酰磷脂酰胆碱（DLPC）侧链相互作用。这些观察结果可以根据头部基团的空间需求来解释，包括电荷排斥和水合作用。其他因素，如质子取代单价阳离子、囊泡表面带电基团的并置以及酰基侧链的长度和不饱和度，都会影响磷脂对胆固醇的亲和力。
