Hydration and stability of sulfatide-containing phosphatidylethanolamine small unilamellar vesicles

The effect of sulfatide on membrane hydration of 1,2-dioleoyl-sn-glycero-3- phosphoethanolamine (DOPE) small unilamellar vesicles (SUVs) was investigat ed using steady-state and time-resolved fluorescence spectroscopy. The degr ee of hydration in the headgroup region of the bilayer lipids was assessed with the fluorescence lifetime of N-(5-dimethylaminonaphthalene-1 -sulfonyl )dipalmitoylphosphatidylethanolamine along with the ratio of its fluorescen ce intensities measured in samples prepared either in D2O- or in H2O-based buffers. Similarly, hydration of acyl chains near the headgroup region and that close to the bilayer center were studied using 1-(4-trimethylammoniump henyl)-6-phenyl-1,3,5-hexatriene and 1-palmitoyl-2-[2-[4-(6-phenyl-trans-1, 3,5-hexatrienyl)phenyl]ethyl]carbonyl]-3-sn-phosphatidylcholine as probes. Increasing sulfatide concentration up to 30 mol% resulted in an increase in surface hydration and a decrease in interchain hydration. These were corre lated with an increase in bilayer stability of the DOPE/sulfatide SUVs. Mor eover, variation of pH was found to affect the hydration and stability of t he bilayer vesicles. No further change in headgroup hydration and interchai n hydration near the bilayer center was observed at sulfatide concentration s greater than or equal to 30 mol%. At such high sulfatide concentrations, bilayer hydration and stability were no longer pH-sensitive. The effects of sulfatide on hydration and stability of DOPE bilayer vesicles are discusse d by taking into account the electrostatic and geometrical properties of th e sulfated galactosyl headgroups. (C) 1999 Published by Elsevier Science B. V. All rights reserved.