Deuterium NMR study of the effect of ergosterol on POPE membranes.
We study the effect of ergosterol on the physical properties of 1-[(2)H(31)]palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) multibilayers using deuterium nuclear magnetic resonance. NMR spectra were taken as a function of temperature and ergosterol concentration up to 70 mol %. The spectral first moments show that there is a dramatic difference in the ability of ergosterol to disorder the gel phase and to order the liquid-crystalline phase of POPE membranes, an unusual behavior among lipid/sterol systems studied up to now. Further investigation of the liquid-crystalline phase shows that ergosterol (erg) increases the chain order of POPE-d31, but that this effect saturates at 10 mol % ergosterol. This is in marked contrast to the effect of cholesterol (chol) on POPE membranes: the chain order of POPE increases with cholesterol to at least 45 mol %. Moreover, we found that at higher ergosterol concentrations (>40 mol %) ergosterol decreases the POPE-d31 chain order, which, to our knowledge, has not been directly observed in other lipid/sterol systems. The temperature-composition phase diagram is presented. Finally, at all ergosterol concentrations, the chain order of liquid-crystalline-phase POPE is much smaller than that of comparable POPE/chol membranes. This implies that there is no liquid-ordered phase behavior for POPE/erg membranes.
Hsueh
Ya-Wei
YW
Department of Physics, National Central University, Jhong-li 320, Taiwan. yhsueh@cc.ncu.edu.tw
Weng
Chi-Jung
CJ
Chen
Mei-Ting
MT
Thewalt
Jenifer
J
Zuckermann
Martin
M
D001703:Biophysics / Q000379:methods*; D002784:Cholesterol / Q000737:chemistry; D003460:Crystallization; D003903:Deuterium / Q000737:chemistry*; D004875:Ergosterol / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry; D008055:Lipids / Q000737:chemistry; D050866:Liquid Crystals; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature
D008051:Lipid Bilayers; D008055:Lipids; D010714:Phosphatidylethanolamines; D002784:Cholesterol; D003903:Deuterium; D004875:Ergosterol