Phospholipid transfer between phosphatidylcholine-taurocholate mixed micelles.

Area of Science:

• Biochemistry
• Physical Chemistry
• Membrane Biophysics

Background:

• Phospholipid transfer proteins facilitate lipid exchange between biological membranes.
• Mixed micelles and vesicles are model systems for studying membrane dynamics.

Purpose of the Study:

• To investigate the kinetics and mechanism of N-(7-nitro-2,1,3-benzoxadiazol-4-yl)phosphatidylethanolamine (N-NBD-PE) transfer between phosphatidylcholine-taurocholate mixed micelles.
• To compare transfer rates between mixed micelles and vesicles.

Main Methods:

• Fluorescence spectroscopy was used to monitor N-NBD-PE transfer.
• Kinetic analysis of initial transfer rates was performed.
• Homologous series of N-NBD-PEs with varying acyl chain lengths were employed.

Main Results:

• Transfer half-times of N-NBD-PEs increased with acyl chain length (11-16 carbons) in mixed micelles (4-35 s).
• Transfer between mixed micelles was 200-6000 times faster than between vesicles.
• Kinetic analysis indicated two main transfer mechanisms: collision-dependent exchange and monomer diffusion.

Conclusions:

• Phospholipid transfer is significantly enhanced in mixed micelles compared to vesicles.
• Enhanced transfer is attributed to transient micelle collisions and faster phospholipid dissociation from mixed micelles.
• The contribution of collision-dependent and monomer diffusion mechanisms increases with acyl chain length and hydrophobicity.