THE INTERACTION OF VARIOUS CHOLESTEROL ANCESTORS WITH LIPID-MEMBRANES - A H-2NMR STUDY ON ORIENTED BILAYERS

The effect of putative cholesterol 'precursors' on model membranes has been studied by deuterium nuclear magnetic resonance (H-2-NMR) spectroscopy. Oriented bilayers were prepared from 1-myristoyl-2-[H-2(27)]myristoyl-sn-glycero-3-phosphocholine (DMPC-d27) and tricyclohexaprenols or octaprenediols. Order parameter profiles were determined and showed that tricyclohexaprenols and octaprenediols increase the acyl chain order in DMPC bilayers, but to a smaller extent than cholesterol. The order parameter increases, depending on the chain position, from 5% to 7% in the presence of ditertiary octaprenediol, and from 16% to 21% in the presence of tricyclohexaprenol-Z,Z. Aqueous multilamellar dispersions of DMPC-d27 and of DMPC-d27 containing 30 mol% tricyclohexaprenol-E,E were prepared, and the first moments calculated from H-2-NMR spectra over the temperature range 5-55-degrees-C. Tricyclohexaprenol-E,E almost abolishes the phase transition of DMPC. Thus, as predicted, tricyclohexaprenols and octaprenediols have a cholesterol-like behaviour in lipid membranes; however their effect on the model DMPC system is weak. On the contrary, isoarborinol has no effect on the lipid chain order in the liquid-crystalline phase of DMPC bilayers. H-2-NMR spectra of aqueous dispersions of DMPC-d27 and 30 mol% isoarborinol between 25 and 60-degrees-C showed the coexistence of two lamellar phases over a wide temperature range, which was confirmed by differential scanning calorimetry (DSC) and P-31-NMR spectroscopy. This absence ot' ordering effect of isoarborinol might bc related to some inherent structural features.