Biophysics Department, Faculty of Science, Cairo University, Giza 12613, Egypt; Department of Physics and Astronomy, College of Science, King Saud University, Riyadh 11451, Saudi Arabia
Interaction between liposomes and protein is important for the structure and function of cells. In the present work, the interaction between collagen and dipalmitoyl phosphatidylcholine (DPPC) liposomes was studied using dielectric spectroscopy technique and rheological measurements. Dielectric data indicated that the DPPC liposomes have strong dielectric dispersion in the frequency range of 50 Hz to 5 MHz. The conductivity and relaxation time increased after addition of collagen to DPPC liposomes. The increase in relaxation time might be attributed to increase in the localized charges distribution within the medium confirmed by the conductivity data. The increase in permittivity over the frequency range tested is an indicator of the interaction between protein and liposomal phospholipid. This is either due to the insertion of collagen into the lipid bilayer via its hydrophobic residues or to adsorption causing a protein layer to be located around liposomes. Interaction between collagen and liposomes increases the liposomal membrane rigidity and increases its microviscosity as indicated from rheological measurements. It was concluded that collagen significantly altered the physical state of liposome membrane, which may be attributed to collagen interaction with liposomes surface and/or by its incorporation within the bilayer membrane.
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