E/M dips. Evidence for lipids regularly distributed into hexagonal super-lattices in pyrene-PC/DMPC binary mixtures...

Area of Science:

• Membrane Biophysics
• Lipid Bilayer Organization
• Fluorescence Spectroscopy

Background:

• Understanding lipid lateral organization is crucial for membrane function.
• Previous studies observed kinks in lipid mixtures, but dips were not reported.

Purpose of the Study:

• To investigate the effect of 1-palmitoyl-2-(10-pyrenyl)decanoyl-sn-glycerol-3-phosphatidylcholine (Pyr-PC) concentration on lipid organization in L-alpha-dimyristoylphosphatidylcholine (DMPC) multilamellar vesicles.
• To analyze the fluorescence E/M ratio for patterns indicating lateral order.

Main Methods:

• Utilized fluorescence spectroscopy to measure the ratio of excimer to monomer fluorescence (E/M).
• Examined Pyr-PC concentration effects in DMPC multilamellar vesicles at 30°C.
• Analyzed the plot of E/M versus mole fraction of Pyr-PC (XPyrPC) for dips and kinks.

Main Results:

• Observed novel dips and kinks in the E/M versus XPyrPC plot, indicating specific lateral ordering.
• Dips and kinks were symmetrically distributed around 50 mol% Pyr-PC.
• Results suggest an extended hexagonal super-lattice model, where both Pyr-PC and DMPC form ordered structures at specific concentrations.

Conclusions:

• The observed dips and kinks provide strong evidence for regular lipid distribution into hexagonal super-lattices in Pyr-PC/DMPC mixtures.
• This finding deepens the understanding of lipid lateral organization in membranes.
• The results pave the way for new theoretical models and experimental designs to explore lipid distribution and membrane functions.