Rapid flip-flop in polyunsaturated (docosahexaenoate) phospholipid membranes.
The transbilayer movement (flip-flop) of 7-nitrobenz-2-oxa-1,3-diazol-4-yl phosphatidylethanolamine (NBD-PE) in phosphatidylcholine (PC) membranes containing various acyl chains was measured by dithionite quenching of NBD fluorescence. Of specific interest was docosahexaenoic acid (DHA), the longest and most unsaturated acyl chain commonly found in membranes. This molecule represents the extreme example of a family of important fatty acids known as omega-3s and has been clearly demonstrated to alter membrane structure and function. One important property that has yet to be reported is the effect of DHA on membrane phospholipid flip-flop. This study demonstrates that as the number of double bonds in the fatty acyl chains comprising the membrane increases, so does the rate of flip-flop of the NBD-PE probe. The increase is particularly marked in the presence of DHA. Half-lives t(1/2) of 0.29 and 0.086 h describe the process in 1-stearoyl-2-docosahexaenoylphosphatidylcholine and 1,2-didocosahexaenoylphosphatidylcholine, respectively, whereas in 1-stearoyl-2-oleoylphosphatidylcholine t(1/2)=11.5h. Enhanced permeability to dithionite with increasing unsaturation was also indicated by our results. We conclude that PC membranes containing DHA support faster flip-flop and permeability rates than those measured for other less-unsaturated PCs.
Department of Biology, Indiana University Purdue University Indianapolis, 46202, USA.
Victoria T
VT
Armstrong
Michael R
MR
Brzustowicz
Stephen R
SR
Wassall
Laura J
LJ
Jenski
William
W
Stillwell
D004281:Docosahexaenoic Acids / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008560:Membrane Fluidity; D008567:Membranes, Artificial; D008968:Molecular Conformation; D009038:Motion; D010713:Phosphatidylcholines / Q000737:chemistry; D010714:Phosphatidylethanolamines / Q000737:chemistry; D010743:Phospholipids / Q000737:chemistry*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence / Q000379:methods
D008051:Lipid Bilayers; D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010743:Phospholipids; D004281:Docosahexaenoic Acids; C042077:N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)phosphatidylethanolamine