Fluorometric investigations of the interaction of polyene antibiotics with sterols.
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Changes in specific fluorescent properties, partial quantum efficiency (PQ), and corrected fluorescence (CO) can be used to monitor the interaction of various polyenes with sterols. The changes in PQ and CO, caused by addition of sterols, are different for each polyene antibiotic. Addition of cholesterol decreases the PQ and CO of filipin in aqueous solution 36 and 62%, respectively, but cholesterol increases the PQ and CO of pimaricin more than 80-fold. Addition of cholesterol to nystatin or amphotericin B has little effect on the fluorescence emission. The filipin complex as well as pimaricin strongly binds sterols that contain both a -hydroxyl group and a long alkyl side chain that is attached to the D ring of sterols. The filipin complex and pimaricin interact weakly or not at all with cholesterol palmitate and 3-keto or 3-hydroxy sterols. The methanol degradation product of filipin (a tetraene epoxide) does not interact with cholesterol. The stoichiometry of the filipin:cholesterol interaction is, within experimental error, 1:1. The interaction of filipin with cholesterol is independent of pH from pH 4.5 to 8, but is dependent on the method of isolation and preparation of the filipin complex. The filipin complex isolated from organic solvents does not interact with sterolsusing fluorescence as a criteria of interactionbut it will interact with sterols after prolonged standing in aqueous solution or heating to 50 for 2 hr. These studies strongly indicate that filipins can exist in conformational states on bonded conditions such as dimers that do not bind sterols in a specific manner and that such forms undergo changes in aqueous solutions to a form or forms that can interact specifically with cholesterol and other -hydroxy sterols. 1972, American Chemical Society. All rights reserved.
