Translocation of phospholipids and dithionite permeability in liquid-ordered and liquid-disordered membranes.
We present a detailed study of the translocation rate of two headgroup-labeled phospholipid derivatives, one with two acyl chains, NBD-DMPE, and the other with a single acyl chain, NBD-lysoMPE, in lipid bilayer membranes in the liquid-disordered state (POPC) and in the liquid-ordered states (POPC/cholesterol (Chol), molar ratio 1:1, and sphingomyelin (SpM)/Chol, molar ratio 6:4). The study was performed as a function of temperature and the thermodynamic parameters of the translocation process have been obtained. The most important findings are 1), the translocation of NBD-DMPE is significantly faster than the translocation of NBD-lysoMPE for all bilayer compositions and temperatures tested; and 2), for both phospholipid derivatives, the translocation in POPC bilayers is approximately 1 order of magnitude faster than in POPC/Chol (1:1) bilayers and approximately 2-3 orders of magnitude faster than in SpM/Chol (6:4) bilayers. The permeability of the lipid bilayers to dithionite has also been measured. In liquid disordered membranes, the permeability rate constant obtained is comparable to the translocation rate constant of NBD-DMPE. However, in liquid-ordered bilayers, the permeability of dithionite is significantly faster then the translocation of NBD-DMPE. The change in enthalpy and entropy associated with the formation of the activated state in the translocation and permeation processes has also been obtained.
Moreno
Maria João
MJ
Departamento de Quimica, Universidade de Coimbra, 3004-535 Coimbra, Portugal. mmoreno@ci.uc.pt
Estronca
Luís M B B
LM
Vaz
Winchil L C
WL
D001692:Biological Transport; D001703:Biophysics / Q000379:methods*; D002462:Cell Membrane / Q000378:metabolism*; D002784:Cholesterol / Q000737:chemistry; D004227:Dithionite / Q000737:chemistry; D019277:Entropy; D006358:Hot Temperature; D007700:Kinetics; D008051:Lipid Bilayers; D010539:Permeability; D010713:Phosphatidylcholines / Q000737:chemistry*; D010743:Phospholipids / Q000737:chemistry*; D021381:Protein Transport; D013816:Thermodynamics
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010743:Phospholipids; D004227:Dithionite; D002784:Cholesterol; C028694:1-palmitoyl-2-oleoylphosphatidylcholine