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Phase behaviour of membrane lipids containing polyenoic acyl chains
W P Williams1, P W Sanderson, B A Cunningham
1Life Sciences Division, King's College London, Campden Hill, UK.
Biochimica Et Biophysica Acta
|June 5, 1993
Summary
Polyenoic lipids like di-18:2 phosphatidylethanolamine exhibit broad, low-enthalpy phase transitions due to loose gel packing. This is linked to reduced van der Waals forces between acyl chains in the gel state.
Area of Science:
- Biochemistry
- Biophysics
- Materials Science
Background:
- Polyenoic lipids, such as di-18:2 phosphatidylethanolamine (di-18:2 PE), display unique low-temperature thermal behaviors.
- Previous studies reported similar transitions in polyenoic phosphatidylcholines and monogalactosyldiacylglycerol (MGDG).
Purpose of the Study:
- To investigate the low-temperature thermal behavior and phase transitions of di-18:2 PE.
- To understand the structural basis for the observed thermal properties in polyenoic lipids.
Main Methods:
- Real-time X-ray diffraction measurements.
- Differential scanning calorimetry (DSC) to analyze thermal transitions and enthalpy changes.
Main Results:
- Di-18:2 PE exhibits broad, low-enthalpy transitions between gel (Lβ) and liquid-crystal (Lα) phases.
- The gel phase of di-18:2 PE is less densely packed compared to lipids with saturated or monoenoic acyl chains.
- Low enthalpy and reduced co-operativity of phase transitions are attributed to diminished van der Waals interactions between acyl chains.
Conclusions:
- The packing of polyenoic lipid acyl chains in the gel state is less ordered due to reduced van der Waals forces.
- Formation of well-ordered lattices in polyenoic lipids may necessitate energy input for hydrogen bond network formation between headgroups.