Influence of cholesterol on the biophysical properties of the sphingomyelin/DOPC binary system |
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Authors: | Hao Y H Chen J W |
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Institution: | (1) National Laboratory of Biomacromolecules, Institute of Biophysics, Academia Sinica, Beijing 100101, China, CN |
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Abstract: | The influence of cholesterol on the sphingomyelin (SM)/dioleoylphosphatidylcholine (DOPC) binary system was investigated
in various respects. Electron spin resonance (ESR) measurements reveal that the order parameter of 5DS (5-doxyl stearic acid)
in SM/DOPC bilayers increases notably when the concentration of cholesterol is over 30 mol%. Membrane potential measurements
indicate that the K+ permeability of the SM/DOPC bilayer decreases steeply at 40 mol% cholesterol concentration. Both these experiments suggest
that cholesterol reduces the motion amplitude of hydrocarbon chains abruptly above 30 mol%. In contrast to the ordering effects
on the hydrocarbon chains, 31P-NMR results indicate that cholesterol slightly increases the motion of phosphate groups of the lipids. 31P-NMR also raises the possibility of domain formation in the presence of cholesterol. Fluorescence-quenching experiments verified
that solid domains appear in the binary system when cholesterol is present, and percolation threshold occurs at 50 mol% cholesterol
concentration. The solid domains bear the properties of liquid ordered phase, which is the basic structure of caveolae and
functional rafts. So this work provides an artificial model for the study of rafts and caveolae on biological membranes.
Received: 29 January 2001/Revised: 17 May 2001 |
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Keywords: | : Electron spin resonance (ESR) — Fluorescence Measurements — 31P-NMR — Percolation Threshold — Liquid Ordered Phase |
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