Stillwell W, Ehringer W D, Dumaual A C, Wassall S R
Department of Biology, Indiana University-Purdue University Indianapolis 46202-5132.
Biochim Biophys Acta. 1994 Sep 15;1214(2):131-6. doi: 10.1016/0005-2760(94)90036-1.
Cholesterol is demonstrated to condense phosphatidylcholine (PC) monolayers and bilayers containing stearic acid in the sn-1 position and alpha-linolenic acid in the sn-2 position (18:0, alpha-18:3 PC) but has no effect when gamma-linolenic acid occupies the sn-2 position (18:0,gamma-18:3 PC). Cholesterol-induced condensation is measured by area/molecule determinations made on monolayers using a Langmuir trough, while condensation in bilayers is followed by the fluorescent dyes merocyanine (MC540) and dansyllysine. Permeability to erythritol is also demonstrated to be diminished by cholesterol for the condensable 18:0,alpha-18:3 PC bilayer membranes but not the 18:0,gamma-18:3 PC membranes. alpha- and gamma-linolenic acid are isomers containing 18 carbons and three unsaturations. Both fatty acids have unsaturations at positions 9 and 12 and differ only in the location of the third unsaturation, at either position 6 for gamma-linolenic acid (an omega-6 fatty acid) and at position 15 for alpha-linolenic acid (an omega-3 fatty acid). Here lipid-cholesterol interaction is used to distinguish the effect of position of unsaturation on membrane structure.
胆固醇可使在sn-1位含有硬脂酸且在sn-2位含有α-亚麻酸的磷脂酰胆碱（PC）单分子层和双分子层（18:0，α-18:3 PC）发生凝聚，但当γ-亚麻酸占据sn-2位时（18:0，γ-18:3 PC）则无此作用。胆固醇诱导的凝聚通过使用Langmuir槽对单分子层进行面积/分子测定来衡量，而双分子层中的凝聚则通过荧光染料部花青（MC540）和丹磺酰赖氨酸来跟踪。对于可凝聚的18:0，α-18:3 PC双分子层膜，胆固醇也可降低赤藓糖醇的渗透性，但对于18:0，γ-18:3 PC膜则无此作用。α-亚麻酸和γ-亚麻酸是含有18个碳原子和三个不饱和键的异构体。两种脂肪酸在9位和12位都有不饱和键，仅在第三个不饱和键的位置上有所不同，γ-亚麻酸（一种ω-6脂肪酸）的第三个不饱和键在6位，而α-亚麻酸（一种ω-3脂肪酸）的第三个不饱和键在15位。在此，脂质-胆固醇相互作用被用于区分不饱和键位置对膜结构的影响。
