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Divalent cation-induced aggregation of chromaffin granule membranes
Membrane Biochemistry
|January 1, 1979
Summary
Cations like calcium aggregate chromaffin granule (CG) membranes by shielding negative charges, with protein interactions driving aggregation. Native CG membranes aggregate faster than artificial ones due to specific protein contacts.
Area of Science:
- Biochemistry
- Membrane Biophysics
- Cell Biology
Background:
- Chromaffin granule (CG) membranes possess negatively charged surfaces, leading to electrostatic repulsion.
- Cation-induced aggregation is crucial for understanding membrane interactions and cellular processes.
Purpose of the Study:
- To investigate the mechanism and kinetics of cation-induced aggregation of chromaffin granule membranes.
- To elucidate the role of proteins and lipids in the aggregation process.
Main Methods:
- Stopped-flow rapid mixing experiments to monitor light-scattering changes.
- Kinetic analysis of dimerization phase using rate constants (kapp).
- Arrhenius plots to determine activation energy.
Main Results:
- Divalent cations induce CG membrane aggregation at millimolar concentrations; monovalent cations require 100-fold higher concentrations.
- Ca2+-induced dimerization rate constant (kapp) is 0.86-1.0 x 10^9 M^-1sec^-1, near diffusion-controlled limits.
- Native CG membranes exhibit significantly faster aggregation rates than artificial lipid vesicles, indicating protein involvement.
Conclusions:
- Cations shield negative surface charges, enabling closer membrane approach.
- Proteins protruding from CG membranes are primary contact points for aggregation.
- Aggregation is further stabilized by hydrogen bonding, cation bridging, and lipid segregation.