Motion and surface accessibility of spin-labeled lipids in a model lipoprotein containing cholesteryl oleate, dimyristoylphosphatidylcholine, and apolipoprotein E.
Motion and surface accessibility of spin-labeled lipids in a model lipoprotein containing cholesteryl oleate, dimyristoylphosphatidylcholine, and apolipoprotein E.
复制标题
含有胆固醇油酸酯、二肉豆蔻酰磷脂酰胆碱和载脂蛋白 E 的模型脂蛋白中自旋标记脂质的运动和表面可及性。
DOI：
10.1021/bi00371a036
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发表时间：
1986
期刊：
影响因子：
2.9
通讯作者：
Morrisett,JD
中科院分区：
文献类型：
--
作者：
Mims,MP;Chari,MV;Morrisett,JD
Symington, F. W., Bernstein, ID, & Hakomori, S.-I.(1984)/. Biol. Chem. 259, 6008-6012. Utsumi, H., Suzuki, T., Inoue, K., & Nojima, S.(1984) J. abstract: A series of spin-labeled phosphatidylcholines (PCs) and cholesteryl esters (CEs) bearing the paramagnetic 2, 2-dimethyloxazolidinyl-1-oxy (doxyl) groupat fatty acyl carbon C5', Cl2', or Cl6'were used to study acyl chain motions in the polar surface shell and hydrophobic core domains of microemulsion (ME) particles containing cholesteryl oleate and dimyristoylphosphatidylcholine (DMPC), and of particles with apolipoprotein E (apoE) bound to their surfaces. Electron paramagnetic resonance data obtained with the doxyl-labeled PCs indicated a gradient of motion in the ME surface monolayer similar to that observed with the same probes in a bilayer. The 5-and 12-doxyl-CEs clearly demonstrated a higher degree of order for the cholesteryl ester rich core than the corresponding doxyl-PCs showed for the phospholipid-richsurface over the entire range 10-60 C. The temperature dependencies of spectra of the 16-doxyl-CE in the core and PC in the surface of the ME were almost identical, suggesting that there was no sharp boundary between core and surface domains. None of the probes detected either the surface phospholipid transition (31 C) or the cholesteryl ester core transition (46 C) measured previously by differential scanning calorimetry and 13C nuclear magnetic resonance. Binding of apoE to spin-labeled DMPC vesicles increased the order of the S'-position of the sn-2 acyl chain over the range 15-33 C; the thermaltransition was broadened and its midpoint elevated. The effect of protein binding was not as striking for the ME particles. In separate studies, the rates of ascorbate-induced reduction of the nitroxyl moietyin ME labeled with either 5-doxyl-PC or 5-doxyl-CE were measured to determine the accessibility of each lipid type to the aqueousphase and the core—* surface mobility of the nonpolar lipids. Reductionof 5-doxyl-PC inthe ME was monophasic; the rates were comparable to those of 5-doxyl-CE in vesicles, but much lower than those of 5-doxyl-PC in vesicles. This result indicated that the C5'-position of thesn-2 acyl chain of PC in the microemulsion was less accessible (by bulk water molecules) than the corresponding position in the vesicle. Reduction of 5-doxyl-CEin the ME was also monophasic and dependent on ascorbate concentration at every temperature studied. Thus, CE movement from the core to the surface was more rapid than the rate of doxyl group reduction. Calculations based on these results suggested that a significantly larger fraction of CEmay be present in the ME surface monolayer than in the vesicle bilayer. e capacity of spin-labeled lipids to detect phase transitions in phospholipid vesicles (Barrett et al., 1969; Hubbell & McConnell, 1971) and neat lipids (Morrisett et al., 1984) is well documented. Binding of peptides or proteins to spin-la-fThis work has beensupported by Specialized Center of Research in Atherosclerosis Grant HL-27341 and by Grant Q-837 from the Robert A. Welch Foundation. MPM is the recipient of National Research Service Award HL-07341 from the National Heart, Lung, and Blood Institute.
