Electrophoretic mobility and zeta potential of liposomes due to arginine and polyarginine adsorption

Abstract

Zeta potential determinations obtained from liposome electrophoretic mobilties provide direct evidence of the Arg orientation in the lipid interphase of phosphatidylcholine and phosphatidilethanolamine bilayers. In addition, the zeta potential of liposomes has also been used to determine the variations of the degree of coverage (θ) of individual liposomes of different lipids and to calculate the dissociation constants and the stoichiometry of the binding.The adsorption of positively charged aminoacids to these membranes deviates from a Langmuir type isotherm with the progressive demethylation of the phosphatidylcholine group suggesting that the adsorption takes place in non independent sites, probably producing surface rearrangements.The cooperative effect observed in dimirystoylphosphatidilethanolamines but not in phosphatidylcholines seems to be related to a reorganization of interfacial water as confirmed by fluorescence spectroscopy using Laurdan as an interphacial probe.It is concluded that that zeta potential measurements provide direct evidence of aminoacid orientation in a lipid interphase giving consistency of the findings suggested by MD and surface spectroscopic studies, congruent with the proposal that the guanidine group is buried in the membrane in a water environment.