Detection of a heat stress-mediated interaction between protein and phospholipid membrane using dielectric measurement

The dielectric response of lipid bilayer membrane vesicles (liposomes) prepared using either phosphatidylcholine from egg (EPC) or 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) was analyzed at a frequency range of 0.1 to 100 MHz. A marked dielectric dispersion for EPC and POPC liposome suspensions was observed above 1 MHz. An appropriate analysis of the dielectric dispersion curve was performed using the Cole-Cole equation and the Debye equation and was found to provide a method for the determination of dielectric parameters. Among the dielectric parameters, the characteristic frequency of a second dispersion around 50 MHz varied corresponding with changes in the test conditions. Of particular note is that an anomalous change in the characteristic frequency in the presence of protein corresponded to the degree of hydrophobic interaction between proteins and liposomes. The value of the frequency around 50 MHz, as well as the decrease in permittivity over the frequency range tested, are indicators of the interaction between proteins and liposomes.