Showing papers on "Membrane lipids published in 1970"
TL;DR: Lipids are classified into soluble and insoluble species and it is suggested, as far as is presently possible, how soluble lipids form mixed micelles with insoluble lipids.
379 citations
TL;DR: A double mutant of Escherichia coli unable to synthesize or degrade unsaturated fatty acids can incorporate fatty acids with various hydrocarbon chain structures into the membrane phospholipids, suggesting a liquid-like state of the lipid phase is required for proper membrane function.
Abstract: A double mutant of Escherichia coli unable to synthesize or degrade unsaturated fatty acids can incorporate fatty acids with various hydrocarbon chain structures into the membrane phospholipids. The temperature characteristic of three physiological properties of cells grown with different fatty acids (growth, respiration, and efflux of thiomethylgalactoside) is compared with the physical properties of the isolated phosphatidylethanolamines in monolayers at an air-water interface. Breaks in the temperature characteristic of the properties measured in vivo correspond to phase transitions in the lipid films from a liquid-expanded to a condensed form. It is concluded that a liquid-like state of the lipid phase is required for proper membrane function.
282 citations
TL;DR: Experimental results presented in this paper support the conclusion that the first region of heat absorption is due to a reversible transition in the lipid component of the membrane, and that the second region isdue to an irreversible denaturation of the protein component.
164 citations
TL;DR: The membrane lipids in living Mycoplasma laidlawii exhibit a phase transition characteristic of that from crystal to liquid crystal within the bilayer conformation, consistent with presence of an extended lipid bilayer in the native membrane.
Abstract: The membrane lipids in living Mycoplasma laidlawii exhibit a phase transition characteristic of that from crystal to liquid crystal within the bilayer conformation. The transition occurs at the same temperature in viable organisms, membranes isolated from the organisms, and isolated membrane lipids. The enthalpy of the transition in the membrane is compared with that of an aqueous suspension of isolated membrane lipids. The result is consistent with presence of an extended lipid bilayer in the native membrane.
144 citations
TL;DR: The results indicate that, in general, the virions acquire the lipid pattern of the plasma membrane of the host cell, and suggest some selective rearrangement of membrane lipids incorporated into virions is possible in some cells.
131 citations
TL;DR: The results indicate that, at least, by far the major part of the nuclear lipids is located in the membranes of thenuclear envelope, which fairly approximates the requirements of a bimolecular lipid leaflet model.
Abstract: The qualitative and quantitative lipid composition of nuclei and nuclear membranes from pig and rat liver were determined. These determinations were compared with the corresponding data obtained for microsomes from the same material after similar treatments. The results indicate that, at least, by far the major part of the nuclear lipids is located in the membranes of the nuclear envelope. The phospholipid pattern of the nuclear membranes and the endoplasmic reticulum (ER) membranes in general is widely identical in both species. As a striking difference in the lipid composition, however, a fourfold increase of esterified cholesterol in the nuclear membranes was found. In a quantitative approach the ratio of total surface area of the nuclear lipids to the total surface area of the nuclear envelope membranes was calculated as being 3.6, a value which fairly approximates the requirements of a bimolecular lipid leaflet model.
99 citations
TL;DR: Findings indicate that the charge on the polar head group of membrane lipids plays an important role in controlling the ion-selective permeability of the bilayer.
Abstract: Bilayer membranes were prepared with the negatively charged lipids phosphatidylglycerol and diphosphatidylglycerol, the positively charged lipid lysyl phosphatidylglycerol, the zwitterionic lipid phosphatidylethanolamine, and an uncharged glycolipid, diglucosyldiglyceride, all isolated from gram-positive bacteria. Bilayer membranes of all these lipids manifested specific resistances of 107 to 109 Ω cm2 and capacitances of 0.3 to 0.4 μF cm−2. The membrane potentials of these bilayers were measured as a function of the sodium chloride, potassium chloride, and hydrogen chloride transmembrane concentration gradients (0.01 to 0.10m) and were found to be linear with the logarithm of the salt activity gradients. Membranes made from lysyl phosphatidylglycerol (one net positive charge) were almost completely chloride selective, whereas membranes from phosphatidylglycerol and diphosphatidylglycerol (one and two net negative charges, respectively) were highly cation selective. Membranes prepared with either diglucosyldiglyceride or phosphatidylethanolamine showed only slight cation selectivity. These findings indicate that the charge on the polar head group of membrane lipids plays an important role in controlling the ion-selective permeability of the bilayer.
95 citations
TL;DR: A spin-labeled fatty acid was incorporated in vivo into the polar lipids of Mycoplasma laidlawii membranes and it is shown that the spin label in the intact membrane is slightly but significantly less mobile than it is in protein-free lipid extracts made from these membranes.
Abstract: A spin-labeled fatty acid was incorporated in vivo into the polar lipids of Mycoplasma laidlawii membranes. The electron paramagnetic resonance signal from either intact cells or their extracted lipids reflected the fatty acid composition of the Mycoplasma membranes. Comparison of signals from intact cells, gramicidin-treated cells, heat-treated cells, and extracted lipids indicates that a major portion of the membrane lipids is in a semiviscous hydrocarbon environment. The results also show that the spin label in the intact membrane is slightly but significantly less mobile than it is in protein-free lipid extracts made from these membranes. Correlated electron microscope examinations using the freeze-etch technique reveal particulate components in the hydrophobic region of the membrane. The mobility of the lipids in the intact cell membrane may be influenced by their association with these particles.
92 citations
TL;DR: The results suggest that the influence of inorganic cations on biological membranes can take place via ion-induced organizational changes in the lipids.
70 citations
TL;DR: Lowering the temperature of growth of Staphylococcus aureus from 37 to 25 C decreased the growth rate and induced changes in the composition of the membrane lipids, suggesting some function for the rubixanthins at suboptimal temperatures.
Abstract: Lowering the temperature of growth of Staphylococcus aureus from 37 to 25 C decreased the growth rate and induced changes in the composition of the membrane lipids. Changes in lipid composition also occur in the transition between exponential and stationary growth phases at one temperature. To isolate the effects of lowering the temperature, exponentially growing S. aureus was abruptly switched from 37 to 25 C by transfer to cooler medium. Exponential growth continued at 25 C without a lag period but with a threefold increase in doubling time. In the period of exponential growth at suboptimal temperature, there was essentially no change in the fatty acid composition of the lipids, little change in the vitamin K2 composition with perhaps a slight increase in the total level, and essentially no change in the phospholipid composition, but a marked stimulation of the synthesis of the rubixanthins. Growth of cells at 25 C was much more sensitive to the inhibition of rubixanthin formation by mixed-function oxidase inhibitors than cells growing at 37 C, suggesting some function for the rubixanthins at suboptimal temperatures. The striking increases in the proportions of monoenoic fatty acids observed at lowered growth temperatures in many biological systems are not detected in S. aureus.
67 citations
TL;DR: Phosphatidylcholine was the least saturated and sphingomyelin the most saturated of the major phospholipids, and cholesterol and free fatty acids were the major constituents of the neutral lipid fraction, accounting for t6 and t3%, respectively, of the total membrane lipids.
TL;DR: The ability to bind selected membrane lipids to membrane proteins of a serologically unrelated species provides a new tool for producing antibodies to lipid haptens.
Abstract: The glycolipid haptens of Mycoplasma pneumoniae were bound to membrane proteins of acholeplasma laidlawii (formerly Mycoplasma laidlawii) by reaggregation. This process consisted of the solubilization of lipid-depleted A. laidlawii membranes and M. pneumoniae glycolipids in 20 mM sodium dodecyl sulfate, and dialysis of the mixed solutions against 20 mM Mg2+. The hybrid reaggregate, collected by centrifugation, was highly immunogenic in rabbits, eliciting the production of a high titer of antibodies that fixed complement with the purified glycolipids and inhibited the metabolism of M. pneumoniae cells. The free glycolipids, or their mixture with A. laidlawii proteins, were much less effective in stimulating these antibodies. The antibodies to the hybrid reaggregate agglutinated M. pneumoniae cells and inhibited their ability to absorb erythrocytes, which indicates that at least some of the serologically-active glycolipids are exposed at the outer membrane surface. The ability to bind selected membrane lipids to membrane proteins of a serologically unrelated species provides a new tool for producing antibodies to lipid haptens.
TL;DR: Electron microscopy of fixed and sectioned material revealed identical structure of original and recombined membranes; both were trilaminar, had an overall thickness of 70–80 A and were found to have an identical granular substructure of the dense layers.
TL;DR: The permeability characteristics of the choroid plexus are qualitatively similar to those of most other cell membranes and there is evidence for the presence of a special mechanism for the transport of sugar across this epithelium.
Abstract: Anin vitro preparation of the frog choroid plexus has been used to measure the permeability of the choroidal epithelium to 50 nonelectrolytes by an osmotic method. The method involves the measurement of nonelectrolyte reflection coefficients (σ) by a rapid electrical procedure. For the majority of compounds tested, there was a good correlation between the rate of solute permeation and the solute's bulk-phase lipid: water partition coefficients; i.e., the higher the partition coefficient the greater the permeability. The membrane lipids of the choroid plexus differ from the membrane lipids of the gall bladder in at least three ways: (1) the lipids of the choroid plexus cannot distinguish between branched chain solutes and their straight chain isomers; (2) small polar solutes such as urea and acetamide permeate via the membrane lipids to a significant extent; and (3) the smaller selectivity ratios suggest that the lipids of the choroid plexus contain more hydrogen bonding sites (i.e., there are stronger solute: lipid intermolecular forces in the choroid plexus). The permeability characteristics of the choroid plexus are qualitatively similar to those of most other cell membranes. In addition, there is evidence for the presence of a special mechanism for the transport of sugar across this epithelium.
TL;DR: Recombinations with individual phospholipids confirm that opposite charges of lipids and proteins are essential for the initial interaction and are considered to be likely that in addition hydrophobic associations between proteins and lipids are formed.
TL;DR: This work has noted that the O-O band intensity in emission is zero and that the radiative life-time calculated from the absorption and fluorescence spectrum is in dramatic disagreement with that derived from measurements of the quantum yield and mean life- time.
TL;DR: The site of lipid incorporation into the membrane was studied by two radioautographic techniques and the membrane lipid was also found, in general, to be conserved in cell growth and division.
TL;DR: It is concluded that growth of the membranes occurs by a mechanism of random intussusception of molecular complexes within different types of preexisting membranes.
Abstract: The development of photosynthetic lamellae during greening of dark-grown Chlamydomonas y-1 cells was investigated by radioautography. Acetate-(3)H was used as a marker for membrane lipids. In short pulse-labeling experiments, about 50-60% of the radioactivity incorporated was found in the lipid fraction and about 25-50% in starch granules present in the chloroplast of these algae. The relative specificity of acetate-(3)H used as a marker for membranes was artificially increased through quantitative removal of the starch granules from fixed cells by amylase treatment. Analysis of turnover coefficients of different membrane constituents and of the contribution of turnover and net synthesis to the total label incorporated in pulse experiments indicated that the incorporation of acetate into specific lipids was mainly due to net synthesis. The distribution of radioactivity in the different lipid constituents at the end of a short pulse and after 30- and 60-min chases indicated that transacylation is minimal and may be disregarded as a possible cause of randomization of the label. Statistical analysis of radioautographic grain distribution and measurements of different structural parameters indicate that (a) the chloroplast volume and surface remain constant during the process, whereas the growth of the photosynthetic lamellae parallels the increase in chlorophyll; (b) the lamellae do not develop from the chloroplast envelope or from the tubular system of the pyrenoid; (c) all the lamellae grow by incorporation of new material within preexisting structures; (d) different types of lamellae grow at different rates. The pyrenoid tubular system develops faster than the thylakoids, and single thylakoids develop about twice as fast as those which are paired or fused to grana. It is concluded that growth of the membranes occurs by a mechanism of random intussusception of molecular complexes within different types of preexisting membranes.
TL;DR: Plasma membranes of rat liver prepared by rate-isopycnic zonal centrifugation suggest that the molecular species of most lipid classes of the same tissue are randomly distributed among cellular organelles, although the class composition may differ significantly betweenorganelles.
TL;DR: The effects of cholesterol upon the molecular packing of erythrocyte and myelin lipids were compared using high resolution NMR and monolayer techniques, indicating that the molecular packings of the isolated lipids are alike.
TL;DR: Evidence in support of the proposed mechanism includes consideration of the structure and degradation of thyroxin, the ability of iodine to exhibit thyromimetic actions, the interaction of iodine with phospholipid model membranes resulting in decreased electrical resistance of the membranes, and the abilityof iodine to lower the activation energy for electrical conduction in lipids in the solid state.
TL;DR: It is suggested that a reduction in the degree of ordered structure of the water molecules at the interphase brings about a correlated increment in lipid mobility which seems to be related to an increased cell permeability (reduction in cell hydrophobicity).
TL;DR: The effects of age and strain of the domestic fowl on the lipid content and composition of the exterior structures of the egg were studied and neutral lipid was found to contain mono-, di- and triglycerides, as well as cholesterol, cholesterol esters and free fatty acids.
TL;DR: The ability to accumulate lipids was investigated in two strains of hydrogen oxidizing bacteria (Hydrogenomonas H 16 and strain 11/x) and it is suggested that there is a true storage of neutral fat in strain 12/x.
Abstract: The ability to accumulate lipids was investigated in two strains of hydrogen oxidizing bacteria (Hydrogenomonas H 16 and strain 11/x). Along with the deposition of poly-β-hydroxybutyrate the amount of other lipids is shown to increase 1.8 times in strain H 16. It is suggested that the increase of the latter lipids is due to the formation of membrane lipids that are needed for the formation of membranes around the intracellular globules of poly-β-hydroxybutyrate. In strain 11/x the amount of lipids increases 7 times along with the storage of carbohydrates. In this case, the majority of lipids consists of triglycerides. It is suggested that there is a true storage of neutral fat in strain 11/x.