1,2-Dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) divalent cation complexes:: an X-ray scattering and freeze-fracture electron microscopy study

被引:21
作者
Garidel, P
Forster, G
Richter, W
Kunst, BH
Rapp, G
Blume, A
机构
[1] Univ Halle Wittenberg, Inst Phys Chem, D-06108 Halle, Germany
[2] Univ Jena, Inst Ultrastruct Res, D-07740 Jena, Germany
[3] LUW, NL-6703 Wageningen, Netherlands
[4] HASYLAB, MPI Colloid & Interface Sci, D-22603 Hamburg, Germany
关键词
D O I
10.1039/b003276j
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
1,2-Dimyristoyl-sn-glycero-3-phosphoglycerol (DMPG) dispersed in 100 mM NaCl at pH 7 forms negatively charged multilamellar vesicles. After addition of divalent cation salts (Mg2+, Ca2+ and Sr2+) in an equimolar cation/lipid ratio, a precipitate of lipid divalent cation (2:1) complexes is formed. These complexes were examined by X-ray diffraction and freeze-fracture electron microscopy to elucidate their phase structure as a function of temperature and incubation time at low temperature. The structural and morphological analysis of the DMPG divalent cation complexes stored for 7 d at 4 degrees C (initial state) revealed the formation of a lamellar phase with a very short lamellar repeat distance of 4.4-4.6 nm. The hydrocarbon chains of the lipid are packed in a subgel state. For all three complexes smooth fracture faces with crystalline appearance were observed in the electron micrographs. Increasing the temperature induces a subgel to liquid-crystalline phase transition at around 58-62 degrees C for the Mg2+ and Sr2+ complexes and at 85 degrees C for the Ca2+ complex. The electron micrographs of the Mg2+ and Sr2+ complexes showed that in the liquid-crystalline phase regular multilamellar vesicles or large multilamellar cylinders are formed, whereas the Ca2+ complex forms lamellar structures of crystalline appearance. At lower temperature (below 35 degrees C), new phases appear: Mg2+ and Sr2+ complexes form a gel-like phase with an increased lamellar repeat distance of similar to 1 nm and a phase transition temperature of about 35 degrees C, whereas the Ca2+ complex transforms into a subgel phase which is very similar to the initial state. Our results show that the interaction of Mg2+ and Sr2+ with DMPG is very similar but different from that observed with Ca2+. The results also indicate interactions of Ca2+ with DMPG in the liquid-crystalline phase, whereas this is not observed for the other two ions.
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收藏
页码:4537 / 4544
页数:8
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