A method for estimating lateral diffusion coefficients in membranes from steady-state fluorescence quenching studies.

Area of Science:

• Biophysics
• Physical Chemistry
• Membrane Science

Background:

• The Stern-Volmer theory is a common model for fluorescence quenching.
• This theory assumes a linear relationship between quencher concentration and fluorescence intensity.
• Its applicability in complex environments like biological membranes is questionable.

Purpose of the Study:

• To evaluate the applicability of the Stern-Volmer theory to fluorescence quenching in membranes.
• To develop and present an alternative empirical method for accurate diffusion coefficient determination.
• To estimate diffusion coefficients of plastoquinone and plastoquinol in liposomes.

Main Methods:

• Numerical analysis of diffusion-controlled quenching in membranes.
• Development of a single-parameter linear approximation for nonlinear concentration curves.
• Least-squares analysis to determine the fitting parameter P.
• Application of the method to pyrene fluorescence quenching in soya bean phosphatidylcholine liposomes.

Main Results:

• Stern-Volmer theory typically overestimates lateral diffusion coefficients in membranes.
• Diffusion-controlled quenching shows nonlinear concentration dependence for specific diffusion coefficients and lifetimes.
• The new empirical method provides accurate estimations of diffusion coefficients.
• Plastoquinone and plastoquinol diffusion coefficients were found to be similar (1.3-3.5 X 10(-7) cm2 s-1).

Conclusions:

• The Stern-Volmer theory is often inadequate for fluorescence quenching studies in membranes.
• The presented empirical method offers a reliable alternative for calculating diffusion coefficients.
• Accurate diffusion measurements are vital for understanding molecular dynamics within lipid bilayers.