Phase properties of liquid-crystalline Phosphatidylcholine/Phosphatidylethanolamine bilayers revealed by fluorescent probes.
The mixing properties of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) were examined in liquid-crystalline phase using fluorescent probes incorporated into lipid bilayers. The excimer to monomer (E/M) fluorescence ratio of 1-hexadecanoyl-2-(1-pyrenedecanoyl)-sn-glycero-3-phosphocholine (PPC) versus PPC concentration was higher for binary mixtures containing phosphatidylcholine (PC)/phosphatidylethanolamine (PE) (1:1) compared to PC matrix. When POPC was gradually replaced with POPE, the E/M ratio also increased suggesting the enhanced lateral mobility or the lateral enrichment of PPC into domains or both. Evidences for the PE-induced domain formation were further provided by resonance energy transfer between 2-(4, 4-difluoro-5-methyl-4-boro-3a, 4a-diaza-s-indacene-3-dodecanoyl)-1-hexadecanoyl-sn-glycero- 3-phospho choline and PPC, which was enhanced as a function of PE concentration, and by the polarization of 1,6-diphenyl-1,3, 5-hexatriene. In addition, PE reduced free volume and polarity of lipid bilayers as measured by the emission fluorescence of 1,2-bis PPC and 6-lauroyl-2-dimethylaminonaphthalene. When POPE analogs with a methylated head group instead of normal POPE were used, the diminished effect on the domain formation was shown in the order N-methyl PE > N,N-dimethyl PE. The results suggest that the mixing properties of POPE and POPC are not random but that lipid domains of phospholipids are formed.
Ahn
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Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Taejon, 305-701, Korea.
Yun
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D015081:2-Naphthylamine / Q000031:analogs & derivatives; D009327:4-Chloro-7-nitrobenzofurazan / Q000031:analogs & derivatives; D004735:Energy Transfer; D005456:Fluorescent Dyes; D007848:Laurates; D008051:Lipid Bilayers / Q000737:chemistry*; D015335:Molecular Probes; D010713:Phosphatidylcholines / Q000737:chemistry*; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence
C095153:1,2-(4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diazaindacene-3-dodecanoyl)-sn-glycero-3-phosphocholine; C078632:1-acyl-2-(12-((7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)dodecanoyl)phosphatidylcholine; D005456:Fluorescent Dyes; D007848:Laurates; D008051:Lipid Bilayers; D015335:Molecular Probes; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; C057561:1-palmitoyl-2-oleoylphosphatidylethanolamine; D015081:2-Naphthylamine; D009327:4-Chloro-7-nitrobenzofurazan; C065580:laurdan