Effects of experimental conditions on the interaction of filipin and pimaricin with cholesterol.

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Abstract
The effect of salts, small neutral molecules, detergents and organic solvents on the interaction of filipin and pimaricin with cholesterol was investigated using fluorometric techniques. The salts and small molecules, at concentrations of 0.5-100 mM, showed no effect on the interaction of filipin with cholesterol. The interaction of pimaricin with cholesterol was slightly decreased in the presence of 100 mM MgCl2 or CaCl2. The detergents sodium deoxycholate and lauryl sulfate altered the fluorescence properties of the polyenes and precluded the interaction of the polyenes with cholesterol. The organic solvents dimethylformamide, ethanol, acetone and iso-propanol when present at 0.1-1% (vol/vol) did not affect the fluorescence properties of pimaricin or the pimaricin-cholesterol complex. These solvents changed the fluorescence properties of filipin and its capacity to interact with cholesterol. These data indicate that low concentrations of some organic solvents and detergents can affect the fluorescence properties of these polyenes in a manner not directly related to the interaction of the polyene with sterol. Light scattering experiments indicate that the different solvents used to solubilize cholesterol produce suspensions of varying size when injected into the aqueous solutions. The extent of the subsequent interaction with the polyene antibiotic correlates with the light scattering properties of these suspensions.