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Lipid lateral diffusion in ordered and disordered phases in raft mixtures.
Andrey Filippov1, Greger Orädd, Göran Lindblom
1Department of Biophysical Chemistry, Umeå University, SE-901 87 Umeå, Sweden.
Biophysical Journal
|January 30, 2004
Summary
Lipid diffusion in complex bilayers reveals distinct liquid disordered and liquid ordered phases. Ordered domains containing sphingomyelin slowly exchange with faster diffusing dioleoylphosphatidylcholine in a lipid sea.
Area of Science:
- Biophysics
- Materials Science
- Physical Chemistry
Background:
- Cell membranes exhibit complex lipid compositions influencing dynamics.
- Understanding lipid phase behavior is crucial for membrane function.
- Quaternary lipid systems offer a more realistic model for biological membranes.
Purpose of the Study:
- To quantify lipid lateral diffusion coefficients in a quaternary system.
- To investigate the phase behavior of dioleoylphosphatidylcholine (DOPC), sphingomyelin, cholesterol, and water mixtures.
- To compare lipid dynamics in quaternary versus ternary systems.
Main Methods:
- Pulsed field gradient nuclear magnetic resonance (PFG-NMR) on aligned bilayers.
- CORE method for global analysis of correlated spectral data.
- System composition: DOPC:sphingomyelin (1:1 molar ratio), 0-45 mol% cholesterol, 40 wt% water, 293-333 K.
Main Results:
- Identified a two-phase region: liquid disordered (l(d)) and liquid ordered (l(o)).
- l(d) phase, rich in DOPC, showed 3-5 times higher diffusion coefficients than l(o) phase.
- Lipid exchange between l(o) and l(d) phases was slow on the millisecond timescale.
Conclusions:
- Quaternary lipid systems exhibit distinct phases with differing lipid mobility.
- Slow inter-phase lipid exchange suggests stable, fluid ordered domains.
- Findings provide insights into membrane domain dynamics and lipid organization.