Barclay L R, Cameron R C, Forrest B J, Locke S J, Nigam R, Vinqvist M R
Department of Chemistry, Mount Allison University, Sackville, Canada.
Biochim Biophys Acta. 1990 Dec 4;1047(3):255-63. doi: 10.1016/0005-2760(90)90524-2.
Cholesterol, when sequestered in saturated liposomes of dimyristoylphosphatidylcholine (DMPC) or dipalmitoylphosphatidylcholine (DPPC), undergoes peroxidation thermally initiated either by a lipid-soluble or a water-soluble azo initiator and in both cases the reaction is inhibited effectively by the water-soluble antioxidant, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylate (Trolox). Quantitative kinetic methods of autoxidation show that the oxidizability, kp/(2kt)1/2 (where kp and 2kt are the rate constants of radical chain propagation and termination, respectively) of cholesterol in DMPC or DPPC multilamellar liposomes, where kp/(2kt)1/2 is 3.0.10(-3) to 4.3.10(-3) M-1/2 s-1/2 at 37-45 degrees C, is similar to that measured in homogeneous solution in chlorobenzene, where kp/(2kt)1/2 is 3.32.10(-3). However, its oxidizability in smaller unilamellar vesicles of DMPC or DPPC increases by at least 3-times that measured in multilamellar systems. Autoxidation/antioxidant methods show that cholesterol partitions directly from the solid state into DMPC or DPPC liposomes by shaking and this is confirmed by 31P and 2H quadrupole NMR spectra of deuterated cholesterol when membrane bound. Analytical studies indicate that up to 21 mol% cholesterol will partition into the membranes by shaking.
胆固醇被包裹在二肉豆蔻酰磷脂酰胆碱（DMPC）或二棕榈酰磷脂酰胆碱（DPPC）的饱和脂质体中时，会通过脂溶性或水溶性偶氮引发剂引发热过氧化反应，在这两种情况下，反应都能被水溶性抗氧化剂6 - 羟基 - 2,5,7,8 - 四甲基色满 - 2 - 羧酸酯（生育三烯酚）有效抑制。自氧化的定量动力学方法表明，在DMPC或DPPC多层脂质体中胆固醇的氧化能力，即kp/(2kt)1/2（其中kp和2kt分别是自由基链增长和终止的速率常数），在37 - 45℃时为3.0×10(-3)至4.3×10(-3) M-1/2 s-1/2，与在氯苯均相溶液中测得的类似，在氯苯中kp/(2kt)1/2为3.32×10(-3)。然而，在DMPC或DPPC较小的单层囊泡中其氧化能力比在多层体系中测得的至少增加3倍。自氧化/抗氧化方法表明，胆固醇通过振荡直接从固态分配到DMPC或DPPC脂质体中，当胆固醇与膜结合时，氘代胆固醇的31P和2H四极核磁共振光谱证实了这一点。分析研究表明，通过振荡，高达21摩尔%的胆固醇会分配到膜中。
