| Flip-flop is the rate-limiting step for transport of free fatty acids across lipid vesicle membranes. | |
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MedLine Citation:
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PMID: 19777995 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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The mechanism of transport of free fatty acids (FFA) across lipid bilayer membranes remains a subject of debate. The debate is whether the rate-limiting step for transport is flip-flop across the membrane or dissociation into the aqueous phase. Recently, a new method for assessing dissociation was described in which fluorescein phosphatidylethanolamine (FPE) introduced into the outer leaflet of lipid vesicles was used to monitor FFA dissociation. Transport of FFA into vesicles containing both FPE in the outer leaflet and pyranine trapped in the inside aqueous phase revealed identical rate constants for quenching of FPE and pyranine fluorescence. Because no difference was observed in the time for FFA binding to the outer surface and flip-flop across the bilayer, it was concluded that dissociation was slower than flip-flop. Here, we used FPE and BSA to assess dissociation of oleate from lipid vesicles. In separate pyranine- or ADIFAB-containing vesicles, we assessed flip-flop. We found that the FPE and BSA transfer methods yielded equivalent rate constants for dissociation, which were 3-10-fold faster than that of flip-flop. We found that in vesicles containing both FPE and pyranine, pyranine fluorescence cannot be separated from FPE fluorescence. The identical rate constants for FPE and pyranine observed with vesicles containing both fluorophores reflected the dominance (20-fold) of FPE fluorescence at pyranine excitation and emission wavelengths. Because the dissociation rate constants are 3-10 times faster than the rate constants for flip-flop, flip-flop must be the rate-limiting step for the transport of FFA across lipid vesicles. |
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Authors:
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Andrew N Carley; Alan M Kleinfeld |
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Publication Detail:
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Type: Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't |
Journal Detail:
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Title: Biochemistry Volume: 48 ISSN: 1520-4995 ISO Abbreviation: Biochemistry Publication Date: 2009 Nov |
Date Detail:
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Created Date: 2009-10-27 Completed Date: 2009-11-17 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 0370623 Medline TA: Biochemistry Country: United States |
Other Details:
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Languages: eng Pagination: 10437-45 Citation Subset: IM |
Affiliation:
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Torrey Pines Institute for Molecular Studies, 3550 General Atomics Court, San Diego, California 92121, USA. |
Export Citation:
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APA/MLA Format Download EndNote Download BibTex |
| MeSH Terms | |
Descriptor/Qualifier:
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Biological Transport
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physiology* Fatty Acids, Nonesterified / chemistry*, metabolism* Fluorescence Kinetics Lipid Bilayers / chemistry*, metabolism* Phosphatidic Acids / chemistry Serum Albumin, Bovine / chemistry, metabolism |
| Grant Support | |
ID/Acronym/Agency:
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DK058762/DK/NIDDK NIH HHS |
| Chemical | |
Reg. No./Substance:
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0/Fatty Acids, Nonesterified; 0/Lipid Bilayers; 0/Phosphatidic Acids; 0/Serum Albumin, Bovine |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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