Vitamin phospholipid bilayers

Liposomes have been used by the pharmaceutical industry to deliver a range of drugs. Liposomes are made of phospholipid bilayers with one of more aqueous compartments depending on whether they are unilamellar, multilamellar, or multivesicular vehicles. Because of the bilayer structures they can adopt, they are versatile vehicles as carriers of water-soluble, oil-soluble as well as amphiphilic components. Hence, they can be used to encapsulate a wide range of food components including flavors, oils, amino acids, vitamins, minerals antimicrobials, and enzymes. Their potential applications in the food industry have been discussed by Mozafari et al. (2008)). Examples of the potential applications of liposomes in food include the delivery of cheese ripening enzymes and natural antioxidants (e.g., vitamin E). 

T. Koga, A. Nagao, J. Terao, K. Sawada, and K. Mukai Synthesis of a phosphatidyl derivative of vitamin E and its antioxidant activity in phospholipid bilayers. Lipids 29 (1994) 83-89. 

First, phospholipid bilayers which mimic cellular membrane and platelet factor 3, on which several blood clotting factors bind in order to generate the more efficient cascade of enzymatic reactions (J ). They are the vitamin K-dependent proteins II, X and IX which are... 

A number of kinetic studies were carried out to elucidate the interaction between a-tocopherol and ascorbic acid in liposomes. By using either water-soluble or oil-soluble diazo radical initiators, the effect of radicals can be compared when they are produced either in the phospholipid bilayer or in the aqueous phase. Oxidation of a soybean phosphatidylcholine liposome in the presence of radicals produced in the water phase with a water-soluble radical initiator [2,2 -azobis(2-amidinopropane) dihydrochloride, (AAPH)], showed an induction period with both a-tocopherol (vitamin E) and ascorbic acid (vitamin C) (Figure 10.9). With a mixture of vitamin E and vitamin C, the length of the induction was close to the sum of the individual induction periods. This result indicates an additive effect in suppressing oxidation by both vitamin E and vitamin C. Vitamin C apparently traps radicals in the water phase. When oxidation was induced by radicals produced in the lipid phase with an oil-soluble radical initiator [2,2 -azobis(2,4-dimethylvaleronitrile), (AMVN)] incorporated into the membrane, ascorbic acid alone had no effect, while a-tocopherol had a greater effect because it is lipophilic. However, the mixture... 

Urano, S., Kitahara, M., Kato, Y., Hasegawa, Y., and Matsuo, M. (1990). Membrane stabilizing effect of Vitamin E existence of a hydrogen bond between alpha-tocopherol and phospholipids in bilayer membranesJ. Nutr. Sci. Vitaminol., 36, 513-519. 

Urano, S. etal., Membrane stabilization of vitamin E interactions of alpha-tocopherol with phospholipids in bilayer liposomes, Biochem. Biophys. Res. Commun., 146, 1413, 1987. 

Hydrophobic protective systems include vitamin E, i.e. a-tocopherol which, as all chromanol compounds, is a free radical scavenger which yields a long-lived radical upon hydrogen abstraction, thereby interrupting the chain reaction [160]. This property is optimized in a-tocopherol (a-TH) which is a remarkable scavenger of peroxyl radicals in phospholipid membrane bilayers [161,162] ... 

A FIGURE 18-12 Model of low-density lipoprotein (LDL). This class and the other classes of lipoproteins have the same general structure an amphipathic shell, composed of a phospholipid monolayer (not bilayer), cholesterol, and protein, and a hydrophobic core, composed mostly of cholesteryl esters or triglycerides or both but with minor amounts of other neutral lipids (e.g., some vitamins). This model of LDL is based on electron microscopy and other low-resolution biophysical methods. LDL is unique in that it contains only a single molecule of one type of apolipoprotein (apoB), which appears to wrap around the outside of the particle as a band of protein. The other lipoproteins contain multiple apolipoprotein molecules, often of different types. [Adapted from M. Krieger, 1995, in E. Haber, ed., Molecular Cardiovascular Medicine, Scientific American Medicine, pp. 31-47]... 

Preparation and characterization of liposomes formed with natural phospholipids were well established. However, in using liposomes for simulation of enzymatic functions, especially in acid-base catalysis, difficulties would be encountered due to their chemicai and morphological instabilities. Thus, bilayer membranes composed of synthetic amphiphiles are more favorable candidates for enzyme mimics. For example, artificial vitamin Bg-dependent enzymes were constructed from catalytic bilayer membranes in combination with a bilayer-forming peptide lipid (10), a hydrophobic vitamin derivative (11), and metal ions (Fig. 5). The catalyst acts as an artificial aminotransferase, showing marked substrate specificity, high enantioselectivity, and turnover behavior for the transamination of a-amino acid with a-keto acids. In addition, the reaction fields provided by the catalytic bilayer membranes are suitable to establish multienzyme systems through functional ahgnments of artificial enzymes and natural ones in a sequential manner. 

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