Differential Properties of the Sterols Cholesterol, Ergosterol, β-Sitosterol, trans-7-Dehydrocholesterol, Stigmasterol and Lanosterol on DPPC Bilayer Order

Abstract

Cholesterol, its precursor lanosterol, the plant sterols β-sitosterol and ergosterol, as well as three further sterols were added up to 50 mol % to vesicles of the phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC). The aim of this study was to investigate the influence of the sterol side chain and ring structure on the acyl chain orientational order of the lipid bilayer by measuring the steady-state fluorescence anisotropy rss of the fluorophore 1-(4-trimethylammonium-phenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) and to establish the molecular basis underlying the changes in order parameter of the lipid bilayer system. Experiments were carried out in the temperature range from 30 to 60 °C, i.e., at temperatures below and above the gel to liquid-crystalline phase transition temperature Tm of DPPC bilayers. In general, the incorporation of the different sterols into the DPPC bilayer enhances the orientational order of TMA-DPH in the liquid-crystalline state of DPPC, whereas the orientationa...