Showing papers on "Membrane lipids published in 1974"
TL;DR: It was found that compositional variation results in the biosynthesis of phospholipids that have identical viscosities at the temperature of growth of the cells, and this "homeoviscous adaptation" can also be observed in E. coli membrane preparations.
Abstract: E. coli incorporates increasing proportions of saturated and long-chain fatty acids into phospholipids as growth temperature is increased. It was found that this compositional variation results in the biosynthesis of phospholipids that have identical viscosities at the temperature of growth of the cells. This “homeoviscous adaptation” can also be observed in E. coli membrane preparations. Viscosities were determined by use of the electron spin resonance spin-label technique.
1,393 citations
TL;DR: This chapter reviews the morphological information on intercellular junctions derived from thin-sectioning, negative staining and freeze-cleave techniques, as well as from x-ray diffraction and biochemical investigations, and correlates the structural parameters with known or proposed physiological functions.
Abstract: Publisher Summary Intercellular junctions are specialized regions of contact between the apposed plasma membranes of adjacent cells, and recent evidence suggests that they are essential for the development of multicellular organisms. They provide the structural means for groups of cells to interact in certain defined ways, and thereby enable them to create structures of higher order. This chapter reviews the morphological information on intercellular junctions derived from thin-sectioning, negative staining and freeze-cleave techniques, as well as from x-ray diffraction and biochemical investigations, and correlates the structural parameters with known or proposed physiological functions. The membrane structure of intercellular junctions is described. Membrane proteins can be divided into two groups: peripheral and integral. Peripheral membrane proteins are believed to be associated with the membrane surface, based on the observation that they are held to the membrane by rather weak noncovalent interactions, and are not strongly associated with membrane lipids. Only mild treatments, such as an increase in ionic strength of the medium or the addition of a chelating agent, are needed to dissociate them molecularly intact from the membrane. Furthermore, in the dissociated state they are relatively soluble in neutral aqueous buffers. In contrast, integral membrane proteins appear much more strongly bound to the lipid matrix, since they can be dissociated from the latter only by drastic treatments with chemicals such as detergents, protein denaturants, and organic solvents. The diversity in structure and function of intercellular junctions offers an exciting field for future research in which morphologists, physiologists, and biochemists should be able to make significant contributions to the knowledge of how individual cells interact to form structures of higher order.
1,292 citations
TL;DR: It is interesting to note that the current membrane model accentuates the fluidity of the membrane, which phospholipids undergo a rapid lateral diffusion within the two monolayers of the bilayer.
296 citations
TL;DR: An appreciable heterogeneity in the physical state of the membrane lipids can apparently be tolerated by this organism without a detectable loss of membrane function.
177 citations
TL;DR: Analysis of autoradiographic analysis of animals injected with tritiated palmitic, stearic, or arachidonic acids supports the conclusion that rods renew the lipids of their outer segments by membrane replacement, whereas both rods and cones renew the membrane lipids by molecular replacement.
Abstract: The renewal of fatty acids in the visual cells and pigment epithelium of the frog retina was studied by autoradiographic analysis of animals injected with tritiated palmitic, stearic, or arachidonic acids. Most of the radioactive material could be extracted from the retina with chloroform-methanol, indicating that the fatty acids had been esterified in lipids. Analysis of the extracts, after injection of [3H]palmitic acid, revealed that the radioactivity was predominantly in phospholipid. Palmitic acid was initially concentrated in the pigment epithelium, particularly in oil droplets which are storage sites for vitamin A esterified with fatty acid. The cytoplasm, but not the nucleus of these cells, was also heavily labeled. Radioactive fatty acid was bound immediately to the visual cell outer segment membranes, including detached rod membranes which had been phagocytized by the pigment epithelium. This is believed to be due to fatty acid exchange in phospholipid molecules already situated in the membranes. Gradually, the concentration of radioactive material in the visual cell outer segment membranes increased, apparently as a result of the addition of new phospholipid molecules, possibly augmented by the transfer from the pigment epithelium of esterified vitamin A. Injected fatty acid became particularly concentrated in new membranes which are continually assembled at the base of rod outer segments. This localized concentration was short-lived, apparently due to the rapid renewal of fatty acid. The results support the conclusion that rods renew the lipids of their outer segments by membrane replacement, whereas both rods and cones renew the membrane lipids by molecular replacement, including fatty acid exchange and replacement of phospholipid molecules in existing membranes.
123 citations
TL;DR: Particle aggregation, induced by lipid phase transition, could also be observed in Streptococcus faecalis membranes, but no aggregation was seen in the fracture faces of some Bacillus species and Staphylococcus aureus, and the non-appearance of aggregation could be explained by the presence of branched-chain fatty acids in the membrane lipids of these bacteria.
122 citations
TL;DR: Antigen mixing, previously shown to be due to diffusion in the plane of the membrane, is retarded when cells are cooled from 37� to 21�C, but is then speeded by further cooling to 15.�C, in accord with observations on phase separations of lipids in artificial and bacterial membranes.
Abstract: Cooling populations of newly formed mouse human heterokaryons has effects on the intermixing of mouse and human surface antigens which indicate the occurrence of phase separations in membrane lipids. Antigen mixing, previously shown to be due to diffusion in the plane of the membrane, is retarded when cells are cooled from 37° to 21°C, but is then speeded by further cooling to 15°C. This result is in accord with observations on phase separations of lipids in artificial and bacterial membranes.
95 citations
TL;DR: Electron spin resonance analysis of suspensions of animal cell plasma membranes consistently reveals four characteristic temperatures for lateral phase separations in the membrane lipids, indicating that some aspect of lipid organization in membranes is destroyed by the extraction procedure.
Abstract: Electron spin resonance analysis of suspensions of animal cell plasma membranes consistently reveals four characteristic temperatures for lateral phase separations in the membrane lipids. Similar analysis of an aqueous dispersion of lipids extracted from these membranes reveals only two characteristic temperatures, indicating that some aspect of lipid organization in membranes is destroyed by the extraction procedure. The characteristic temperatures for surface membranes from two different species of homeothermic animals were nearly identical and were approximately 37°, 31°, 21°, and 15°. A treatment of the physical data revealed that these temperatures could identify independent phase transitions for two hydrocarbon compartments of approximately equal size with lower and upper characteristic temperatures of 21° and 37°, and of 15° and 31°. The analysis of the effects of temperature on a number of physiological parameters indicates that 21° and 37° are likely to define the boundaries for lateral phase separations in the inner monolayer and 15° and 31° the boundaries for lateral phase separations in the outer monolayer.
95 citations
TL;DR: The viral membrane is made more fluid by proteolytic digestion of the viral glycoproteins, and the possible role of this viral protein-mediated alteration of the physical state of membrane lipids in the maturation of Sindbis virions is discussed.
90 citations
TL;DR: In this article, a nonlinearity in the changes of viscosity with temperature was found in sonicated human erythrocyte membranes at 18-19 °C, and it was inferred that the break observed in the membranes correspond to the transition temperature of the lipids.
88 citations
TL;DR: Experimental evidence indicates that adamante lowers the transition temperatures detected from the temperature dependence of the motion of spin labels and from the Arrhenius plots of O 2 uptake, which infers that membrane-dependent physiological functions are dependent upon the physical state of membrane lipids.
TL;DR: Findings suggest a model for how changes in the cell membrane may account for some of the characteristic differences observed between contact-inhibited and transformed cells.
Abstract: Studies on contact-inhibited mouse embryo fibroblast 3T3 cells and 3T3 cells transformed by oncogenic RNA and DNA viruses and by a chemical carcinogen have demonstrated differences in plasma membrane architecture. Spin-label and freeze-fracture ultrastructural studies have shown that contact-inhibited cells have ordered membrane lipids and aggregated intramembranous particles, whereas transformed cells have fluid membrane lipids and randomly distributed intramembranous particles. These findings suggest a model for how changes in the cell membrane may account for some of the characteristic differences observed between contact-inhibited and transformed cells.
TL;DR: The results suggest that carotenoid pigments rigidify the Acholeplasma membrane and the organism maintains its membrane fluidity within a narrow range by modifying the fatty acyl composition of the membrane lipids.
TL;DR: The experimental results indicate that, in addition to membrane lipids, vicinal water may be involved in this phase transition in active dry yeast reconstituted in water at 38–42°C.
TL;DR: The ability of iodide ions added to one side of a lipid bilayer to quench the fluorescence of the sterol sterophenol on that side of the bilayer is utilized, to measure sterol ‘flipflop’ in liposo mes.
TL;DR: The experimental approaches to the study of the initial events of endocytosis, the possible involvement of microfilaments, and the possible role of membrane lipids in the events of membrane fusion are discussed.
Abstract: A brief description of endocytosis and exocytosis is followed by a discussion of the experimental approaches to the study of the initial events of endocytosis, the possible involvement of microfilaments, and in particular the possible role of membrane lipids in the events of membrane fusion. Recently developed model systems are also discussed.
TL;DR: X-ray diffraction patterns show that extracted erythrocyte membrane lipids from which almost all cholesterol has been removed undergo a rigid crystalline to liquid crystalline transition over the range 2 to 20°C, but these results do not substantiate the indications of a phase transition at 18° to20°C.
TL;DR: Sodium dodecylsulfate-polyacrylamide gel electrophoresis and lactoperoxidase-catalyzed protein radio-iodination were used to compare the structure of the liver endoplasmic reticulum (microsomes) from control, phenobarbital-, and 3-methylcholantrene-pretreated rats and a model is proposed for the mechanism of insertion of the induced proteins into the microsomal membrane.
TL;DR: Different synthetic lipids (mainly lecithins) with characteristic transition temperatures T,.
TL;DR: The action of chlorhexidine closely resembles that of CTAB, following an all-or-none pattern, and the possibility that the disruptive effect of positive surfactants is due to their penetration of the region of the glycerol moieties of membrane lipids is discussed.
TL;DR: Functional anomalies observed in this disease, such as the impairment in sarcoplasmic reticulum calcium uptake or the changes in the ATPase activity of the sarcolemma5, can be related to the lipid disorder.
Abstract: TISSUES from patients with Duchenne muscular dystrophy1 (DMD) as well as animals with similar inherited2 or experimentally produced3 disorders have been shown to undergo significant changes in the amount and composition of their membrane lipids. Most pronounced are the increases in cholesterol and sphingomyelin and the decrease in phosphatidyl choline levels. Functional anomalies observed in this disease, such as the impairment in sarcoplasmic reticulum calcium uptake4 or the changes in the ATPase activity of the sarcolemma5, can be related to the lipid disorder.
TL;DR: The present study examines the extent to which the fatty acid composition of the membrane lipid can be altered by nutritional means in mutants of Escherichia coli defective in total fatty acid synthesis, compared to those observed in wild type cells subjected to the same conditions of fatty acid supplementation.
TL;DR: The drastic changes in the lipid composition found after overloading with Triton WR 1339 confirm that the plasma membrane participates in the formation of the secondary lysosomal membrane.
TL;DR: In this paper, the authors reported remarkable features of endogenously produced retina FFAs, showing that they arise from membrane lipids, and that a different behavior is apparent in the rate of release of individual FFAs from the tissue in vitro.
TL;DR: An appreciable heterogeneity in the physical state of the membrane lipids can apparently be tolerated by this organism without a detectable loss of membrane function.
Abstract: The physical state of the membrane lipids, as determined by fatty acid composition and environmental temperature, has a marked effect both on the temperature range within which A. laidlawii can grow and on the temperature coefficient of growth within the permissible temperature range. The minimum growth temperature under certain conditions is clearly defined by the lower boundary of the gel–to–liquid-crystalline phase transition of the membrane lipids. The physical state of the membrane lipids can also influence the optimum and maximum growth temperatures. An a brupt increase in the temperature coefficient of growth is noted at temperatures between the phase transition boundaries. Both the absolute rates and the temperature coefficients of cell growth are similar for cells whose membrane lipids exist entirely or predominantly in the liquid-crystalline state, but absolute growth rates decline rapidly and temperature coefficients increase when most of the membrane lipids become solidified. Some cell growth, however, can continue at temperatures at which less than 10% of the total lipid remains in the fluid state. Conversion of the membrane lipid from the liquid-crystalline to the gel state is accompanied by a progressive aggregation of intramembranous protein particles. An appreciable heterogeneity in the physical state of the membrane lipids can apparently be tolerated by this organism without a detectable loss of membrane function.
TL;DR: Cholesterol uptake by Acholeplasma laidlawii membranes was unaffected by the removal of 75% of the membrane protein by pronase digestion, indicating that the major portion of the cholesterol bound to the mycoplasma membrane is incorporated into its lipid domain.
TL;DR: The recent studies on the uptake of cholesterol by isolated mycoplasma membranes indicated that the lipid domain of the membrane is the main element responsible for cholesterol uptake, while membrane proteins contribute little to cholesterol binding.
TL;DR: Studies of the fluorescent emission spectra of ANS and the effect of chaotropic perturbants on the motion of perylene suggest that the bilayer structure in vesicles of unfractionated lipids is distorted in such a way as to allow for the penetration of more water molecules near the hydrophobic region or to induce the probes to be nearer to the aqueous phase than is the case for the polar lipids alone.
TL;DR: Tetrahymena pyriformis is qualified as a potentially rewarding model system for studying the process of membrane assembly because of marked differences in rates of lipid and protein labeling.
TL;DR: Experiments with autoxidation of linoleate, haemolysis of red blood cells, lipid peroxidation in macrophages, and in vivo effects of antioxidants on collagen produced by quartz injected subcutaneously have shown that per oxidation of membrane lipids is not the primary mechanism whereby quartz attacks membranes.