Kinetics of Protein-Induced Flocculation of Phosphatidylcholine Liposomes

The influence of protein adsorption on membrane−membrane interactions was studied regarding the kinetic stability of phosphatidylcholine (PC) liposome dispersions. The rates of flocculation were measured by the decrease in the transmitted light intensities in time. To elucidate the experimental data, we proposed an analytical method relating light transmittance to the average size of liposome flocs. The obtained relaxation time and maximum light absorbance were connected to the kinetic constant and the flocculation activation energy. These model parameters were calculated for the flocculation processes of PC liposomes in the presence of lysozyme, cytochrome c, and bovine serum albumin as a function (i) of the protein concentration and (ii) of the ionic strength. In addition to the generally accepted concept that the stability of PC liposomes is due to the action of hydration repulsive force, here we found that in the presence of soluble proteins the steric factors and electrostatics play essential roles for the colloidal stability of egg PC liposome dispersions.