Structure and Thermotropic Behaviour of Mixed Choline Phospholipid Model Membranes
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Phosphatidylcholines and sphingomyelins are among the most abundant lipids in mammalian cell membranes, being major components of platelets or erythrocytes, and of the lipid monolayer of lipoproteins. General efforts have been devoted to the elucidation of the interaction of the ubiquitous membrane component cholesterol with these choline phospholipids, but fewer studies have been reported on the interaction between the phospholipids themselves. A gel to liquid-crystalline phase transition was observed for pure sphingomyelin liposomes at physiological temperature, while palmitoyloleoyl phosphatidylcholine adopts a liquid-crystalline phase in the temperature range 273–323 K. The two phospholipids are miscible at all molar ratios in the liquid-crystalline phase, characterized by very similar lamellar repeat distances for all binary lipid mixtures. The gel phase of pure sphingolipid liposomes exhibited a markedly smaller lamellar repeat distance as compared to mixed lipid vesicles, which increased slightly with temperature for the pure sphingomyelin (66.9–69.2 Å). Concomitantly, altered hydrocarbon chain packing was observed. Similar diffractograms were obtained in the presence of 10 mol% phosphatidylcholine. However, in the composition range between 20 and 60 mol% phosphatidylcholine in the phosphatidylcholine–sphingomyelin admixture, the lamellar repeat distance in the gel phase was markedly increased and remained almost constant (around 75 Å) below the phase transition.Keywords:
Thermotropic crystal
Lamellar phase
The lamellar structure of a thermotropic aromatic polyester with flexible spacer has beenstudied by using transmission electron microscopy. It was found that the lamellar structure couldbe observed in the crystalline samples of this semirigid polymer crystallized from different states.The thickness of lamellae is around 10 nm, which is similar to that of the conventional polymersof flexible chain molecules. The molecular chains in the lamellae are oriented in the thicknessdirection as determined by electron diffraction. The possibility of molecular chains folding in the lamellae has been discussed.
Thermotropic crystal
Folding (DSP implementation)
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Thermotropic crystal
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The lamellar structure of a thermotropic aromatic polyester with flexible spacer has beenstudied by using transmission electron microscopy. It was found that the lamellar structure couldbe observed in the crystalline samples of this semirigid polymer crystallized from different states.The thickness of lamellae is around 10 nm, which is similar to that of the conventional polymersof flexible chain molecules. The molecular chains in the lamellae are oriented in the thicknessdirection as determined by electron diffraction. The possibility of molecular chains folding in the lamellae has been discussed.
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Folding (DSP implementation)
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Abstract Cultures of newborn rat heart myocytes undergo major age-related alterations as demonstrated by comparing 5-6-day-old cells (young cells) and 14-15-day-old cells (old cells). This includes: changes from spherical to elongated shape; sphingomyelin and cholesterol level/cell increase by 100% and 50%, respectively, while the phosphatidylcholine is reduced by 15-20% with almost no change in content of total phospholipids. There is a 50% increase in total protein content/cell while DNA content remain constant. The specific activity of seven marker enzymes representing most subcellular organelles is increased. Beating rate is reduced from 160 +/- 20 to 20 +/- 20 beats min-1. All the above age-dependent alterations are affected by modification of cellular polar lipid composition. Small unilamellar vesicles of egg phosphatidylcholine added to the growth medium of old cells serve as donor of egg phosphatidylcholine to the cells and as acceptor of cellular sphingomyelin and cholesterol. Sphingomyelin-phospholipid exchange can be separated from cholesterol depletion either by using vesicles of egg phosphatidylcholine/cholesterol mixtures which serve only in the phospholipid exchange process, or by small unilamellar vesicles of sphingomyelin which act only as efficient cholesterol acceptors. Such experiments indicated that the major response of old cells is to alteration in the phosphatidylcholine to sphingomyelin mole ratio, while changes in the cholesterol level induce smaller effects. Thus, reversal of phosphatidylcholine to sphingomyelin mole ratio to the values shown by young cells reverse cellular functions and features which were altered by cell aging to levels found in young cells. This includes: increase in the beating rate back to 160 +/- 20, reduction in the total protein level and in the specific activity per DNA content of seven marker enzymes and reappearance of spherical cell shape. These results suggest that membrane lipid composition has major influence on cellular properties which as described in the accompanying paper (Yechiel, E., Barenholz, Y., and Henis, Y. I. (1985) J. Biol. Chem. 260, 9132-9136), may be mediated through the organization and dynamics of the cell membranes.
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The lipid composition of membranes of erythrocytes in athletes of cyclic types of sport with qualification from first adult class to Master of Sports and persons doing no sports was analyzed. The qualitative and quantitative analysis of phospholipid fractions and fatty-acid specter of sphingomyelin and phosphatidylcholine was implemented. In athletes, amount of sphingomyelin and phosphatidylcholine and percentage content of phosphatidylcholine were significantly increased. The percentage content of kefalin was also decreased. The ratio of sphingomyelin/phosphatidylcholine was lower on 52.3%. In fatty-acid specter of sphingomyelin and phosphatidylcholine of athletes the percentage of C14:0 and C16:0 was decreased. In phosphatidylcholine increase of content of C16:1 was noted and in sphingomyelin content of C18:3 was increased. The ratio of sums of saturated fatty acids/ polyunsaturated fatty acids were lower in athletes. The study results testify significant alterations in membranes of erythrocytes caused by regular physical loads and probably favoring increase of functional activity.
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The lipid composition of membranes of erythrocytes in athletes of cyclic types of sport with qualification from first adult class to Master of Sports and persons doing no sports was analyzed. The qualitative and quantitative analysis of phospholipid fractions and fatty-acid specter of sphingomyelin and phosphatidylcholine was implemented. In athletes, amount of sphingomyelin and phosphatidylcholine and percentage content of phosphatidylcholine were significantly increased. The percentage content of kefalin was also decreased. The ratio of sphingomyelin/phosphatidylcholine was lower on 52.3%. In fatty-acid specter of sphingomyelin and phosphatidylcholine of athletes the percentage of C14:0 and C16:0 was decreased. In phosphatidylcholine increase of content of C16:1 was noted and in sphingomyelin content of C18:3 was increased. The ratio of sums of saturated fatty acids/polyunsaturated fatty acids were lower in athletes. The study results testify significant alterations in membranes of erythrocytes caused by regular physical loads and probably favoring increase of functional activity.
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