Dielectric response of cells and liposomes and its utilization for evaluation of cell membrane-protein interaction

The dielectric measurements of an Escherichia coli (E. coli) cell suspension and liposome suspensions were carried out in the frequency range between 0.1 and 100 MHz to detect the heat stress-mediated interaction between proteins and cell membranes. The dielectric relaxation dispersion was observed to be above 1 MHz. The dielectric parameter (amplitude of dispersion, deltaepsilon) based on the Cole-Cole equation was anomalously changed with increasing temperature. The value of deltaepsilon of liposomes was varied at various temperatures depending on the type of protein present. The change in deltaepsilon of liposomes correlated with the amount of protein translocated across the phospholipid membrane. The changes in the value of deltaepsilon of E. coli cells with temperature variation was similar to those of liposomes in the presence of proteins, suggesting that the variation in dielectric parameters reflected the interaction between the phospholipid membrane and proteins. It was found that the dielectric measurement could be utilized for the detection of the interaction between proteins and liposomes.