ACTION OF MELITTIN ON THE DPPC-CHOLESTEROL LIQUID-ORDERED PHASE - A SOLID-STATE H-2-NMR AND P-31-NMR STUDY

Solid-state deuterium and phosphorus-31 nuclear magnetic resonance stu dies of deuterium-labeled beta-[2,2',3,4,4' ,6-H-2(6)]-cholesterol and 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine have ben undertaken to monitor the action of melittin on model membranes containing 30 mol % cholesterol, both at the molecular and macroscopic level. Cholestero l totally inhibits the toxin-triggered formation of large unilamellar vesicles and strongly restricts the appearance of small discs. The lat ter remain stable over a wide temperature range (20-60 degrees C) beca use of an increase in their cholesterol content as the temperature inc reases. This process is related to a constant disc hydrophobic thickne ss of similar to 29 Angstrom. The system, when not in the form of disc s, appears to be composed of very large vesicles on which melittin pro motes magnetically induced ellipsoidal deformation. This deformation i s the greatest when the maximum of discs is observed. A model to descr ibe both the disc formation and stability is proposed.