Transbilayer and interbilayer phospholipid exchange in dimyristoylphosphatidylcholine/dimyristoylphosphatidylethanolamine large unilamellar vesicles
- Univ. of Virginia, Charlottesville (USA)
The rates of spontaneous interbilayer and transbilayer exchange of ({sup 3}H)dimyristoylphosphatidylcholine (({sup 3}H)DMPC) were examined in the DMPC and DMPC/dimyristoylphosphatidylethanolamine (DMPE) large unilamellar vesicles in the liquid-crystalline-, gel-, and mixed-phase states. DMPC desorption rates from either gel or liquid-crystalline phases containing DMPE are very similar to the corresponding rates from pure DMPC gel or liquid-crystalline phases. The authors proposed that the DMPC/DSPC behavior results from packing defects in gel phases composed of both DMPC and DSPC molecules because of the four-carbon difference in the acyl chain lengths of the two species. The present results strongly support this hypothesis because no such anomalous behavior is observed in DMPC/DMPE, which is similar to DMPC/DSPC in phase behavior but does not have the chain length difference. These results are not consistent with lipid headgroup dehydration as the major energetic barrier to flip-flop but rather suggest that the spontaneous formation of fluctuation defects and the energetics of a lipid passing through or being part of such a defect may be the limiting factors. A mechanistic model is proposed. Finally, some predictions based on the model are made and experimentally tested for the related process of bilayer permeation by protons. The permeation results were found to be entirely consistent with the model.
- OSTI ID:
- 5596239
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 30:6; ISSN 0006-2960; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
CELL CONSTITUENTS
CELL MEMBRANES
ESTERS
HYDROGEN COMPOUNDS
LIPIDS
MEMBRANES
MOLECULAR STRUCTURE
ORGANIC COMPOUNDS
ORGANIC PHOSPHORUS COMPOUNDS
PERMEABILITY
PH VALUE
PHASE STUDIES
PHOSPHOLIPIDS
TEMPERATURE DEPENDENCE
TRITIUM COMPOUNDS