Journal
BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES
Volume 1463, Issue 2, Pages 439-447Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/S0005-2736(99)00236-9
Keywords
free fatty acid; lipid bilayer; molecular packing; phase transition; ion transport
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Funding
- NIGMS NIH HHS [GM 28120, GM 30969] Funding Source: Medline
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We measured the influence of saturated and unsaturated free fatty acids on the permeability and partition of ions into 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) bilayers. The bilayer permeability was measured using the depletion of N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-1,2-dihexadecanoyl-sn-glycero-3-phosphatidylethanolamine (N-NBD-PE) fluorescence as a result of its reduction by dithionite. We observed a distinct increase of dithionite permeability at the main gel-fluid phase transition of DMPC. When vesicles were formed from a mixture of DMPC and oleic acid, the membrane permeability at the phase transition was reduced drastically. Stearic acid and methyl ester of oleic acid have little effect. Similar results in the quenching of pyrene-PC in DMPC vesicles by iodide were obtained. Again, the increase of iodide partition into the lipid phase at the main phase transition of DMPC was abolished by the addition of unsaturated free fatty acids. Free fatty acids, in concentrations up to 5 mol%, do not abolish DMPC phase transition when measured by differential scanning calorimetry. It seems that unsaturated, but not saturated, free fatty acids reduce the lipid bilayer permeability to dithionite and iodide ions at the main phase transition of DMPC, without altering the thermodynamic properties of the bilayer. (C) 2000 Elsevier Science B.V. All rights reserved.
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