FLAVONOLS - NEW FLUORESCENT MEMBRANE PROBES FOR STUDYING THE INTERDIGITATION OF LIPID BILAYERS

Two flavonols, 3-hydroxy-4'-dimethylaminoflavone (FME) and 3-hydroxy-4 '-(15-azacrown-5) flavone (FRC) have been investigated as new fluoresc ence probes for studying the formation of the interdigitated gel phase in lipid bilayers. The formation of the interdigitated gel phase in t he saturated symmetrical phosphatidylcholines (PCs) and phosphatidylet hanol (Peth) in the presence of ethanol has been well studied. The pre sent study examines the behavior of these new probes in PC-ethanol and Peth-ethanol systems, as well as in PC-cholesterol and Peth-cholester ol vesicles. The present results demonstrate that both flavonols give distinctively different spectra in interdigitated lipids compared to n on-interdigitated lipids, when examined in lipids in which the interdi gitation behavior is known. This makes them useful for determinations of the structural state of unknown lipids, and for following the trans itions between interdigitated and non-interdigitated phases. However, in the presence of cholesterol, only FCR gave appropriate indications of interdigitation. The results with FME in the presence of cholestero l were not consistent with the known behavior of the lipids examined; instead, FME appears to be located preferentially in the cholesterol-r ich non-interdigitated regions of the bilayer. (C) 1998 Elsevier Scien ce B.V.