Prodan as a membrane surface fluorescence probe: partitioning between water and phospholipid phases

Area of Science:

• Biophysics
• Membrane Biophysics
• Fluorescence Spectroscopy

Background:

• 6-propionyl-2-dimethylaminonaphthalene (Prodan) is a fluorescent probe used to study phospholipid bilayers.
• The spectral properties of Prodan are sensitive to environmental polarity, similar to Laurdan.
• Understanding probe partitioning is crucial for accurate membrane characterization.

Purpose of the Study:

• To investigate the fluorescence spectral features of Prodan in phospholipid vesicles across different phase states.
• To develop a method for separating Prodan fluorescence contributions from the lipid phase and aqueous environment.
• To determine Prodan's partitioning behavior between phospholipid bilayers and water, and between different lipid phases.

Main Methods:

• Steady-state fluorescence spectroscopy (excitation and emission spectra).
• Application of a novel three-wavelength generalized polarization method.
• Analysis of spectral shifts attributed to dipolar relaxation and probe partitioning.

Main Results:

• Prodan spectra exhibit sensitivity to environmental polarity and dipolar relaxation.
• The three-wavelength method successfully separates Prodan fluorescence from lipid and water phases.
• Prodan preferentially partitions into the liquid-crystalline phase over the gel phase.
• Prodan's partition coefficient is dependent on the phospholipid phase state and bilayer packing.
• Prodan detects polarity variations nearer the bilayer surface compared to Laurdan.

Conclusions:

• Prodan is a valuable probe for studying membrane phase transitions and surface polarity.
• The developed method enhances the accuracy of Prodan-based membrane studies.
• Prodan's partitioning behavior provides insights into lipid bilayer organization and dynamics.