title: Transbilayer and interbilayer phospholipid exchange in dimyristoylphosphatidylcholine/dimyristoylphosphatidylethanolamine large unilamellar vesicles.
abstract: The rates of spontaneous interbilayer and transbilayer exchange of [3H]dimyristoylphosphatidylcholine ([3H]DMPC) were examined in 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. This is not the case for DMPC desorption from distearoylphosphatidylcholine (DSPC)-containing gel phases, where the desorption rates are significantly faster than from a pure DMPC gel phase [Wimley, W. C., & Thompson, T. E. (1990) Biochemistry 29, 1296-1303]. We 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. The inclusion of 10-30 mol % DMPE in DMPC bilayers was also found to have a significant effect on the rate of transbilayer movement (flip-flop) of [3H]DMPC in the liquid-crystalline phase. Between 10 and 30 mol % DMPE, flip-flop of DMPC is slowed by at least 10-fold relative to flip-flop in DMPC bilayers, and the entropy and enthalpy of flip-flop activation are both substantially decreased.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biochemistry, University of Virginia, Charlottesville 22903.
authors.forename: W C
authors.initials: WC
authors.lastname: Wimley
authors.forename: T E
authors.initials: TE
authors.lastname: Thompson
mesh_terms: D002250:Carbon Radioisotopes; D002788:Cholesterol Esters / Q000737:chemistry; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D007700:Kinetics; D008051:Lipid Bilayers; D008081:Liposomes; D008433:Mathematics; D008954:Models, Biological; D010539:Permeability; D010714:Phosphatidylethanolamines / Q000737:chemistry*; D013816:Thermodynamics; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D002788:Cholesterol Esters; D008051:Lipid Bilayers; D008081:Liposomes; D010714:Phosphatidylethanolamines; D014316:Tritium; C014409:cholesteryl oleate; D004134:Dimyristoylphosphatidylcholine; C018525:1,2-dimyristoylphosphatidylethanolamine