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Originally published as Biophys J. BioFAST on April 14, 2006.
doi:10.1529/biophysj.106.082115
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Biophysical Journal 91:873-881 (2006)
© 2006 The Biophysical Society

Translocation of Phospholipids and Dithionite Permeability in Liquid-Ordered and Liquid-Disordered Membranes

Maria João Moreno, Luís M. B. B. Estronca and Winchil L. C. Vaz

Departamento de Quimica, Universidade de Coimbra, 3004-535 Coimbra, Portugal

Correspondence: Address reprint requests to Prof. Maria João Moreno, Departamento de Quimica, Universidade de Coimbra, 3004-535 Coimbra, Portugal. Tel.: 351-239-854481; Fax.: 351-239-827703; E-mail: mmoreno{at}ci.uc.pt.

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 ~1 order of magnitude faster than in POPC/Chol (1:1) bilayers and ~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.






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Copyright © 2006 by the Biophysical Society.