Document Detail


High-pressure freezing causes structural alterations in phospholipid model membranes.
MedLine Citation:
PMID:  9674157     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
The influence of high-pressure freezing (HPF) on the lipid arrangement in phospholipid model membranes has been investigated. Liposomes consisting of pure dipalmitoyl-phosphatidylcholine (DPPC) and of DPPC mixed with a branched-chain phosphocholine (1,2-di(4-dodecyl-palmitoyl)- sn-glycero-3-phosphocholine) have been analysed by freeze-fracture electron microscopy. The liposomes were frozen either by plunging into liquid propane or by HPF. The characteristic macroripple-phase of the two-component liposome system is drastically changed in its morphology when frozen under high-pressure conditions. The influence of ethanol which acts as pressure transfer medium was ruled out by control experiments. In contrast, no high-pressure alterations of the pure DPPC bilayer membrane have been observed. We assume that the modification of the binary system is due to a pressure-induced relaxation of a stressed and unstable lipid molecule packing configuration. HPF was performed with a newly designed sample holder, for using sandwiched copper platelets with the high-pressure freezing machine Balzers HPM010. The sandwich construction turned out to be superior to the original holder system with regard to freeze-fracturing of fluid samples. By inserting a spacer between the supports samples with a thickness of 20-100 microns can be high-pressure frozen. The sandwich holder is provided with a thermocouple to monitor cooling rates and allows exact sample temperature control. Despite a two-fold mass reduction compared to the original holder no HPF cooling rate improvement has been achieved (4000 degrees Cs-1). We conclude that the cooling process in high-pressure freezing is determined mainly by cryogen velocity.
Authors:
K Semmler; J Wunderlich; W Richter; H W Meyer
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of microscopy     Volume:  190     ISSN:  0022-2720     ISO Abbreviation:  J Microsc     Publication Date:  1998 Jun 
Date Detail:
Created Date:  1998-08-18     Completed Date:  1998-08-18     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0204522     Medline TA:  J Microsc     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  317-27     Citation Subset:  IM    
Affiliation:
Institute of Ultrastructure Research, Friedrich-Schiller-University Jena, Germany.
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MeSH Terms
Descriptor/Qualifier:
1,2-Dipalmitoylphosphatidylcholine / analysis
Cryopreservation / methods*
Freeze Fracturing / methods*
Lipid Bilayers*
Liposomes*
Microscopy, Electron
Phospholipids / chemistry*
Pressure
X-Ray Diffraction
Chemical
Reg. No./Substance:
0/Lipid Bilayers; 0/Liposomes; 0/Phospholipids; 2644-64-6/1,2-Dipalmitoylphosphatidylcholine

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