Perturbation of phospholipid bilayers by DDT

Area of Science:

• Biochemistry
• Membrane Biophysics
• Lipid Bilayer Dynamics

Background:

• Understanding how environmental factors affect cell membrane properties is crucial.
• Phosphatidylcholines like DPPC and egg PC are key components of biological membranes.
• DDT (dichlorodiphenyltrichloroethane) is a known environmental contaminant with potential membrane interactions.

Purpose of the Study:

• To investigate the localization of DDT's effects on acyl chain dynamics in phosphatidylcholine bilayers.
• To determine how DDT concentration influences membrane fluidity and structure.
• To examine DDT's impact on the phase transition temperature of lipid bilayers.

Main Methods:

• Steady-state fluorescence polarization using n-(9-anthroyloxy) fatty acid probes at various depths.
• Investigated unilamellar vesicles of DPPC and egg PC with varying DDT concentrations (5-50 mol%).
• Measured changes in microviscosity and fluorescence lifetime.

Main Results:

• DDT acts as a fluidizer for both DPPC and egg PC bilayers.
• Increased microviscosity in DPPC bilayers at 23°C initiated at the bilayer center and progressed outward with increasing DDT.
• DDT (33 mol%) reduced the phase transition temperature of DPPC bilayers by ~2°C; no significant effect on fluorescence lifetime observed.

Conclusions:

• DDT's fluidizing effect is localized and concentration-dependent within lipid bilayers.
• The impact of DDT on membrane microviscosity differs between gel and fluid phases.
• DDT does not significantly alter the excited-state fluorescence lifetime of probe molecules in these lipid systems.