Proton decay kinetics for vesicles containing buffers-an analytical solution

Area of Science:

• Biochemistry
• Physical Chemistry
• Membrane Biophysics

Background:

• Vesicles with high internal proton concentration require understanding of efflux kinetics.
• Internal buffers significantly influence proton concentration decay rates.
• Transmembrane electric potential is assumed to be zero for simplified analysis.

Purpose of the Study:

• To derive an analytical solution for predicting proton efflux and internal proton concentration decay in buffered vesicles.
• To investigate the role of internal buffers in modulating proton gradient equilibration.
• To simplify kinetic analysis under specific pH conditions.

Main Methods:

• Developed an analytical solution for proton efflux kinetics.
• Assumed proton diffusion as the primary mechanism for proton activity equilibration.
• Defined six key physical parameters for a single-buffer system.

Main Results:

• Internal buffers increase the time for proton concentration equilibration.
• Under specific conditions (pH > pK + 1), kinetics follow pseudo first-order reactions.
• Apparent rate constants are influenced by membrane permeability, buffer concentration, and pK.

Conclusions:

• The derived analytical solution accurately predicts proton efflux and concentration decay.
• Internal buffer concentration is a critical factor in determining proton efflux half-time.
• The model shows good agreement with experimental data from thylakoid vesicles.