Phospholipid lateral organization in synthetic membranes as monitored by pyrene-labeled phospholipids: effects of temperature and prothrombin fragment 1 binding.
Pyrene-labeled phospholipids have been used to test for the existence of lateral domains due to temperature-induced phase separations and binding of prothrombin fragment 1 to charged lipid vesicles. When in close proximity, pyrene-containing probes can exchange excited-state energy to form excimers; the ratio of the excimer to monomer fluorescence intensity (E/M) is proportional to the local concentration of probe in the membranes, as well as to the excimer lifetime and the probe's lateral diffusion coefficient. The ability of the pyrene-labeled phospholipids to quantitatively report the coexistence of multiple environments was demonstrated in dipalmitoylphosphatidylcholine/palmitoyloleoylphosphatidylcholine multilamellar vesicle preparations of varying compositions, each of which contained coexisting fluid and gel phases. In this system, pyrene-labeled phosphatidylcholine was found to favor the fluid relative to the gel phase with a partition coefficient of 7. At 37 degrees C, in dioleoylphosphatidylglycerol (DOPG)/palmitoyloleoylphosphatidylcholine (POPC) large, unilamellar vesicles containing either pyrene-labeled phosphatidylglycerol (py-PG) or pyrene-labeled phosphatidylcholine (py-PC), the excimer lifetime (37 ns) and the lateral diffusion constant of the probe (5.8 X 10(-8) cm2/s) were independent of the membrane composition and the presence of fragment 1 and Ca2+. Consequently, E/M was directly proportional to only the local concentration of the py-PG or py-PC probes. When saturating amounts of fragment 1 and 5 mM Ca2+ were added to DOPG/POPC vesicles that contained either probe, no change in E/M and hence the local probe concentration was observed.(ABSTRACT TRUNCATED AT 250 WORDS)
D000818:Animals; D002417:Cattle; D007700:Kinetics; D008081:Liposomes; D010446:Peptide Fragments / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000378:metabolism; D010715:Phosphatidylglycerols / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D011485:Protein Binding; D011498:Protein Precursors; D011516:Prothrombin / Q000378:metabolism*; D011721:Pyrenes; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
D008081:Liposomes; D010446:Peptide Fragments; D010713:Phosphatidylcholines; D010715:Phosphatidylglycerols; D010743:Phospholipids; D011498:Protein Precursors; D011721:Pyrenes; C029733:prothrombin fragment 1; D011516:Prothrombin