Biomaterial Database

The interaction of alpha-tocopherol and homologues with shorter hydrocarbon chains with phospholipid bilayer dispersions. A fluorescence probe study. 1988

V E Kagan, and P J Quinn

Department of Biochemistry, King's College London, England.

The intrinsic fluorescence of tocopherol homologues with hydrocarbon chains ranging from 1 carbon (C1) to 16 carbons (alpha-tocopherol, C16) and their ability to quench the fluorescence of 9-anthroyloxy derivatives of fatty acids with the fluorophore located at different positions in the hydrophobic domain of phospholipid bilayers has been used to model the interaction of tocopherol with lipid bilayer membranes. All the tocopherol homologues used, C1, C6, C11 and alpha-tocopherol, showed a similar fluorescence emission intensity at 325 nm in cyclohexane but were almost completely self-quenched by aggregation in water. Fluorescence was restored when dispersions of dimyristoylglycerophosphocholine were added but the maximum intensity was lower with the longer-chain homologues. Full intensity was observed in all homologues on addition of the detergent Triton X-100. Studies using 9-anthracenecarboxylic acid and 9-anthracenecarboxymethyl ester, 6-(9-anthroyloxy)stearic acid and 16-(9-anthroyloxy)palmitelaidic acid showed that the tocopherol homologues partitioned into the hydrophobic domain of phospholipid dispersions composed of dimyristoylglycerophosphocholine at 40 degrees C and dioleoylglycerophosphocholine at 40 degrees C. The 9-anthroyloxy fatty acids and 1,6-diphenyl-1,3,5-hexatriene were quenched by all the homologues and Stern-Volmer plots of the concentration dependence of the quenching indicated that this was predominantly via dynamic processes. No fluorescence energy transfer was observed between diphenylhexatriene and tocopherols but efficient transfer was recorded to the 9-anthroyloxy fatty acid probes. The results are consistent with a model in which the chromanol nucleus of tocopherol is oriented towards the lipid-water interface of the phospholipid bilayer. As the phytol chain length increases there is an increasing tendency for the chromanol nucleus to reside in the hydrophobic interior of the structure. alpha-Tocopherol appears to form clusters within the phospholipid dispersion which are not fluorescent and do not quench the fluorescence of the different fluorescent probes nor transfer fluorescence energy to them. It is suggested that the monomeric form is responsible for the vitamin effects of tocopherol and the aggregated form acts as a reservoir that does not markedly perturb bilayer stability.

UI	MeSH Term	Description	Entries
D008051	Lipid Bilayers	Layers of lipid molecules which are two molecules thick. Bilayer systems are frequently studied as models of biological membranes.	Bilayers, Lipid,Bilayer, Lipid,Lipid Bilayer
D010743	Phospholipids	Lipids containing one or more phosphate groups, particularly those derived from either glycerol (phosphoglycerides see GLYCEROPHOSPHOLIPIDS) or sphingosine (SPHINGOLIPIDS). They are polar lipids that are of great importance for the structure and function of cell membranes and are the most abundant of membrane lipids, although not stored in large amounts in the system.	Phosphatides,Phospholipid
D004735	Energy Transfer	The transfer of energy of a given form among different scales of motion. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed). It includes the transfer of kinetic energy and the transfer of chemical energy. The transfer of chemical energy from one molecule to another depends on proximity of molecules so it is often used as in techniques to measure distance such as the use of FORSTER RESONANCE ENERGY TRANSFER.	Transfer, Energy
D001665	Binding Sites	The parts of a macromolecule that directly participate in its specific combination with another molecule.	Combining Site,Binding Site,Combining Sites,Site, Binding,Site, Combining,Sites, Binding,Sites, Combining
D013050	Spectrometry, Fluorescence	Measurement of the intensity and quality of fluorescence.	Fluorescence Spectrophotometry,Fluorescence Spectroscopy,Spectrofluorometry,Fluorescence Spectrometry,Spectrophotometry, Fluorescence,Spectroscopy, Fluorescence
D014810	Vitamin E	A generic descriptor for all TOCOPHEROLS and TOCOTRIENOLS that exhibit ALPHA-TOCOPHEROL activity. By virtue of the phenolic hydrogen on the 2H-1-benzopyran-6-ol nucleus, these compounds exhibit varying degree of antioxidant activity, depending on the site and number of methyl groups and the type of ISOPRENOIDS.