Stoichiometry of interaction of the polyene antibiotic, filipin, with free and liposomal-bound cholesterol

Abstract

The polyene antibiotic, filipin, is known to interact with cholesterol present in aqueous solutions, artificial membranes and sterol-containing biological membranes. The stoichiometry of interaction between filipin and free or liposomal-bound cholesterol present in an aqueous system was determined by quantitating the ultraviolet spectral change of filipin which occurs in the presence of cholesterol. A preliminary analysis of the data obtained from aqueous dispersions of cholesterol + filipin alone suggested that the stoichiometry was 1:1. According to a more refined analysis of this same data by the Scatchard technique, there are 1.11±0.18 molecules of cholesterol associated with filipin in this system. Additionally it was found in a liposome solution consisting of lecithin: dicetylphosphate: [4‒14C]-cholesterol that the maximum spectral change of filipin only occurred where a 1:1 ratio of filipin: sterol was present. Thus the likely stoichiometry of the filipin-cholesterol complex in both these systems is 1:1. A procedure is described wherein the sterol-mediated spectral-change of filipin can be utilized as the basis of a sensitive assay for quantitating the amounts of sterol in membrane fractions. © 1974, JAPAN ANTIBIOTICS RESEARCH ASSOCIATION. All rights reserved.