Kinetics of Protein-Induced Flocculation of Phosphatidylcholine Liposomes

Abstract

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.

Size Dependence of Protein-Induced Flocculation of Phosphatidylcholine Liposomes

“…4. The relative activation energy, E * * , was estimated on the basis of experimentally attainable parameters from light scattering measurements and the application of a previously reported analytical method (12). From the initial rate of flocculation, V = K n 2 , where n is the liposome concentration, the rate constant, K , of the protein-induced flocculation of phosphatidylcholine liposome dispersions can be determined.…”

“…In addition, the adsorption of LSZ and CC induces PC liposome bridging flocculation (11,12). The activation energy and the rate of the protein-induced liposome flocculation (PILF) depend strongly on the protein/lipid concentration ratio, ionic strength (12), and ambient temperature (13).…”

“…We have estimated the changes in the rate and activation energy of LSZ-or CC-induced flocculation by varying the liposome radius in the range 50-500 nm. The changes in the rate constant and the activation energy of protein-induced liposome flocculation have been determined experimentally by measuring the light absorbance shift with time and applying a previously reported analytical model (12).…”

Estudio del efecto de β-caroteno en el mecanismo de desactivación de oxígeno singlete en células mamíferas

“…Los carotenoides también cumplen su rol como antioxidantes en la eliminación de radicales como se demostró para los radicales fenoxilo (32).…”

“…Los cationes radicales carotenoides resultantes de las reacciones de ET tienen tiempo de vida del orden de los milisegundos y absorben en la región del infrarrojo cercano alrededor de 1000 nm (32,34,35).…”