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Showing papers on "Membrane lipids published in 1977"


Journal ArticleDOI
TL;DR: Two images of the cell membrane are presented — as a sea of lipid with islands of protein and as a matrix of protein with lakes of lipid, both of which suggest that zones of fluid lipid within the membrane form the environment for membrane proteins.
Abstract: Early in this century, colloid chemists debated about whether cells were bounded by a surface membrane. Today, they debate about the organization of molecules within that membrane. The research involved has led to two images of the cell membrane — as a sea of lipid with islands of protein and as a matrix of protein with lakes of lipid. Both concepts suggest that zones of fluid lipid within the membrane form the environment for membrane proteins. Much of this lipid is in the form of a bilamellar leaflet with hydrophilic portions that face the aqueous environment on either side and . . .

413 citations


Journal ArticleDOI
TL;DR: The preparation of polyene fatty acid membrane probes cis- and trans-parinaric acid and parinaroylphosphatidylcholines and their use in studies of several one- and two- component lipid systems are described and several rates are observed in the binding process which are interpreted as rapid outer monolayer uptake and a much slower process of interlamellar exchange.
Abstract: The preparation of polyene fatty acid membrane probes cis- and trans-parinaric acid and parinaroylphosphatidylcholines and their use in studies of several one- and two- component lipid systems are described. The fluorescence quantum yield of trans-parinaric acid in dipalmitoylphosphatidylcholine at 20 degrees C is approximately 0.3; the quantum yield in aqueous solution is negligibly small. Thermal-phase transitions in single-component phospholipid dispersions are monitored with absorption and fluorescence excitation peak position, fluorescence intensity, lifetime, and polarization. The transition temperatures observed are consistent with previous determinations. Shifts in the absorption peak position are related to the bilayer expansion as it undergoes the gel to liquid-crystalline transition, while fluorescence depolarization provides semiquantitative information concerning molecular motion of the probe in the bilayer. A long fluorescence lifetime component is observed for parinaric acid in the solid phase (up to 50 ns), and a short lifetime component is observed (ca. 5 ns) in the fluid phase of dipalmitoylphosphatidylcholine; both lifetime components are observed in the transition region. In most phospholipids, cis-parinaric acid detects the melting transition at about 1 degree C lower than trans-parinaric acid. Partitioning experiments involving mixed populations of phospholipid vesicles show that trans-parinaric acid preferentially associates with solid-phase lipids, while cis-parinaric acid shows a more equal distribution between solid and fluid lipids. The binding of cis-parinaric acid to dipalmitoylphosphatidylcholine at 25 degrees C is described as partitioning of parinaric acid between lipid vesicles and the aqueous phase with a partition coefficient of 5 X 10(5). Several rates are observed in the binding process which are interpreted as rapid outer monolayer uptake and a much slower process of interlamellar exchange. The phase diagram of the binary lipid mixture dipalmitoylphosphatidylcholine-dipalmitoylphosphatidylethanolamine has also been examined and found to be essentially identical to the one constructed using a nitroxide probe.

318 citations


Journal ArticleDOI
TL;DR: Combined histochemical and biochemical studies confirm earlier reports demonstrating a shift from polar to neutral lipid during cornification and suggest that granular layer polar lipid, through as yet undefined mechanisms, may be transformed into the neutral lipids of the cornified layer.

281 citations


Journal ArticleDOI
03 Mar 1977-Nature
TL;DR: The abiotic synthesis of various lipids, including membranogenic phospholipids, are reported here, which are obvious candidates for prebiotic membrane components.
Abstract: IT is generally agreed that stable membranes were prerequisite to the assembly of the earliest self-replicating systems1–4. Phospholipids, which are ubiquitous in biological membranes and which self-assemble in aqueous environments into stable lipid bilayers and vesicles4, are obvious candidates for prebiotic membrane components. We report here the abiotic synthesis of various lipids, including membranogenic phospholipids.

213 citations


Journal Article
TL;DR: Lipid metabolism of the parasite may be associated with alterations in the amounts of octadecenoic fatty acids and cholesterol in the erythrocyte plasma membrane, which in turn are responsible for changes in permeability and fragility.
Abstract: Merozoite endocytosis initiates Plasmodium development in a vacuole bounded by an erythrocyte-derived membrane, whose asymmetrical distribution of lipids and proteins is reversed in its orientation with respect to the parasite plasma membrane. Reorientation may accompany the proliferation of the membrane associated with the parasite's growth and phagocytic and pinocytic feeding. Increases in the membrane surface area of the parasite, and in some cases of the erythrocyte, parallel parasite growth and segmentation. Augmentation of all the membrane systems of the infected erythrocyte causes the lipid content to rise rapidly, but the parasite lipid composition differs from that of the erythrocyte in many respects: it is higher in diacyl phosphatidylethanolamine, phosphatidylinositol, polyglycerol phosphatides, diacylglycerols, unesterified fatty acids, triacylglycerols, and hexadecanoic and octadecenoic fatty acids and lower in sphingomyelin, phosphatidylserine, alkoxy phosphatidylethanolamine, cholesterol, and polyunsaturated fatty acids. Active lipid metabolism accompanies the membrane proliferation associated with feeding, growth, and reproduction. Plasmodium is incapable of de novo biosynthesis of fatty acids and cholesterol; however, it can fabricate its glycerides and phosphoglycerides with host-supplied fatty acids, nitrogenous bases, alcohols, ATP, and coenzyme A, and can generate the glyceryl moiety during glycolysis. Cholesterol is obtained from the host but nothing is known of sphingolipid origins. Lipid metabolism of the parasite may be associated with alterations in the amounts of octadecenoic fatty acids and cholesterol in the erythrocyte plasma membrane, which in turn are responsible for changes in permeability and fragility.

202 citations


Journal ArticleDOI
TL;DR: It is used as a model for the interactions of the polypeptide segments of transmembrane proteins within the hydrocarbon region of the lipid bilayers of biomembrane structures and the various results are discussed to provide insight pertinent to the organisation, interactions, aggregation properties, boundary layer and packing arrangements of helicalpolypeptides and proteins in reconstituted systems and natural biomemBRanes.

193 citations


Journal ArticleDOI
TL;DR: Rat intestinal microvillus membranes and lipid extracts prepared from them have been studied by fluorescence polarization with three lipid-soluble fluorophores, confirming the localization of the last compound to the hydrophobic interior of the membrane, relatively distant from the Hydrophilic head groups of the polar lipids.
Abstract: Rat intestinal microvillus membranes and lipid extracts prepared from them have been studied by fluorescence polarization with three lipid-soluble fluorophores: diphenylhexatriene, retinol, and anthroyl-stearate. The degree of fluorescence polarization of diphenylhexatriene, which provides an index of the "microviscosity" of the lipid regions of the membrane, is exceptionally high in microvillus membranes, the highest yet reported in normal biological membranes. Both the membrane proteins and lipids were found to contribute to the high values. With each of the three probes the polarization values are higher in ileal microvillus membranes as compared to membranes from proximal intestinal segments. Temperature-dependence studies of the fluorescence polarization of diphenylhexatriene and anthroylstearate demonstrate a phase transition in microvillus membranes and in liposomes prepared from their lipid extracts at approximately 26+/-2 degrees C. Ambient pH influences markedly the diphenylhexatriene fluorescence polarization in microvillus membranes but has little effect on that of human erythrocyte ghost membranes. The "microviscosity" of jejunal microvillus membranes is maximal at pH 6.5-7.0 and decreases as much as 50% at pH 3.0, an effect which depends largely upon the membrane proteins. Addition of calcium ions to suspensions of microvillus membranes increases the fluorescence polarization of retinol and anthroyl-stearate, but not that of diphenyl-hexatriene. This confirms the localization of the last compound to the hydrophobic interior of the membrane, relatively distant from the hydrophilic head groups of the polar lipids. Microvillus membrane proteins solubilized with Triton X-100 give relatively high fluorescence polarization and intensity values with retinol, suggesting the presence of binding proteins which could play a role in the normal absorptive mechanism for the vitamin.

186 citations


Journal ArticleDOI
TL;DR: Certain molecular packing criteria previously employed in a quantitative analysis of lipid micelles and bilayers are here extended to biological membranes, pointing to a highly complex self-assembly mechanism in which the organization of lipids and proteins is highly coupled.

178 citations


Book ChapterDOI
TL;DR: Experimental evidence indicates that the membrane lipids not only create a barrier to the free entry and exit of molecules into and out of the cell, but lipids also provide a matrix in/on which biochemical reactions can take place; through which certain metabolites can pass selectively; and with which recognition, adhesion, aggregation and fusion of cells can be mediated.
Abstract: Publisher Summary The central problem of membrane structure and its correlation with physiological and biochemical functions is to define the organization of constituent molecules. The existence of bilayers in biomembranes is established by a variety of physicochemical techniques. It has been shown that the subtleties of organizational and phase characteristics of the bilayer arise from the segmental motion and the transverse, rotational, and lateral mobilities of constituent lipids. These molecular features of lipids in the bilayer organization account for dielectric, viscoelastic, partitioning, and passive permeability characteristics. Experimental evidence indicates that the membrane lipids not only create a barrier to the free entry and exit of molecules into and out of the cell, but lipids also provide a matrix in/on which biochemical reactions can take place; through which certain metabolites can pass selectively; and with which recognition, adhesion, aggregation and fusion of cells can be mediated.

177 citations


Journal ArticleDOI
TL;DR: Mouse peritoneal macrophages incubated in serumless medium containing a 19:0 or trans-18:1 fatty acid complexed to bovine serum albumin incorporate the exogenous fatty acid supplement into cellular phospholipids, suggesting that the degree of lipid fluidity of macrophage membranes influences both phagocytosis and pinocytotic in macrophaging.
Abstract: Mouse peritoneal macrophages incubated in serumless medium containing a 19:0 or trans-18:1 fatty acid complexed to bovine serum albumin incorporate the exogenous fatty acid supplement into cellular phospholipids. Within 8 hr, 25% of the total phospholipid fatty acids are derived from the supplement, with cell viability remaining greater than 95%. The incorporation of either of these supplements increases the saturated/unsaturated fatty acid ratio in the phospholipids 2-fold over that of cells cultured in serum and effects striking changes in endocytic activities. The levels of both fluid-phase pinocytosis and receptor-mediated phagocytosis are decreased at all temperatures examined between 15 degrees and 37 degrees. The increased degree of saturation of cell phospholipids correlates with decreased endocytic rates for both processes and with increased activation energies (Eact) for phagocytosis. The Eact values for phagocytosis, which range from 54 to 90 kcal/mol, depend on the supplementation conditions used. Although the levels of pinocytosis are depressed, the Eact values for pinocytosis (17--25 kcal/mol) are not strikingly affected by saturated fatty acid enrichment. These observations suggest that the degree of lipid fluidity of macrophage membranes influences both phagocytosis and pinocytosis in macrophages.

162 citations


Journal ArticleDOI
TL;DR: The diversity of compounds examined which caused these changes indicates that no single catabolic pathway is involved, and many of the observed changes are consistent with the hypothesis that cells adapt their membrane lipids to compensate for the presence of these compounds in the environment.
Abstract: Cells of Escherichia coli contain an altered fatty acid and phospholipid composition when grown in the presence of sublethal concentrations of a variety of organic solvents and food additives. The diversity of compounds examined which caused these changes indicates that no single catabolic pathway is involved. Many of the observed changes are consistent with the hypothesis that cells adapt their membrane lipids to compensate for the presence of these compounds in the environment. Both sodium benzoate and calcium propionate caused the synthesis of unusual fatty acids.

Journal ArticleDOI
22 Sep 1977-Nature
TL;DR: Human HLA-A, B, C and Ia antigens were labelled by lactoperoxidase-catalysed iodination of the inner surface of lymphocyte plasma membrane and thus are transmembrane proteins, and membrane-bound human IgM and mouse IgM, IgD and Thy-1 antigen were not labelled on the inner membrane surface.
Abstract: Human HLA-A, B, C and Ia antigens were labelled by lactoperoxidase-catalysed iodination of the inner surface of lymphocyte plasma membrane and thus are transmembrane proteins. In contrast, membrane-bound human IgM and mouse IgM, IgD and Thy-1 antigen were not labelled on the inner membrane surface.

Journal ArticleDOI
28 Jul 1977-Nature
TL;DR: New evidence is presented concerning the anaesthetic properties of the n-alkanes which points to the bilayer as the site of action and also suggests a mechanism for the inhibition of impulse propagation.
Abstract: IT is generally accepted that neutral anaesthetics, such as the n-alkanols and n-alkanes, act from a hydrophobic site1. Discussion has tended to focus on the nature of this site and, particularly, whether it is located in a membrane protein or in the interior of a bilayer2,3. If the site is in a bilayer then the question arises as to how the proteins involved in nervous impulse propagation are affected. We present here new evidence concerning the anaesthetic properties of the n-alkanes which points to the bilayer as the site of action and also suggests a mechanism for the inhibition of impulse propagation. Briefly, the cut-off in anaesthetic potency on ascending the homologous series is found to be closely related to the decrease in adsorption of the alkane into a cholesterol-containing bilayer. In addition, the anaesthetic hydrocarbons produce a concentration-dependent increase in bilayer thickness. On the basis of these two observations, and from our knowledge of the properties of the ion channel-forming polypeptide gramicidin A (ref. 4) we propose that a thickening of the bilayer regions of the nerve membrane by the alkanes destabilises the open ionic channels formed during electrical excitation.

Journal ArticleDOI
TL;DR: In an attempt to understand the mechanism by which a structural change of membrane lipids affects transport functions, the temperature dependence of transport rate has been measured to below the low temperature end of the fluid in equilibrium ordered phase transition of the membrane Lipids.
Abstract: In an attempt to understand the mechanism by which a structural change of membrane lipids affects transport functions, the temperature dependence of transport rate has been measured to below the low temperature end of the fluid in equilibrium ordered phase transition of the membrane lipids. The unsaturated fatty acid requiring Escherichia coli strain T105 was supplemented with either trans-delta9-octadecenoate or trans-delta9-hexadecenoate or supplemented with and subsequently starved for cis-delta9-octadecenoate. Fluid in equilibrium ordered phase transitions measured in whole cells using the fluorescence probe N-phenyl-1-naphthylamine were compared with the temperature dependence of beta-glucoside and beta-galactoside transport. In addition to the previously observed downward "break" in the Arrhenius plot of transport rate which occurred near the middle of the phase transition temperature range, a second upward "break" was observed which could be correlated with the low-temperature end of the phase transition. These experiments are interpreted in terms of a partitioning of transport proteins between ordered and fluid domains which is described by a lateral distribution coefficient, k. This distribution coefficient varies with the membrane lipid composition as well as with the transport system. Values for k suggest a 2-20-fold preference for the partitioning of transport proteins into the fluid parts of the membrane.

Journal ArticleDOI
TL;DR: The rate of transmembrane movement is at least 30,000 times faster than the rate of spontaneous diffusion (flip-flop) of phosphatidylethanolamine across artificial phospholipid bilayers, indicating that transmemBRane movement must be a facilitated process in living cells, perhaps involving membrane proteins.
Abstract: The transbilayer distribution of phospholipids in Bacillus megaterium is asymmetrical, with twice as much phosphatidylethanolamine internally as externally (Rothaman, J E & Kennedy, E P (1977) J Mol Biol 110,603-618) We now report that the biosynthesis of phosphatidylethanolamine is also asymmetrical Newly synthesized phosphatidylethanolamine was found first on the cytoplasmic side of the membrane of pulse-labeled cells and later was redistributed until the specific radioactivity of the outer face became equal to that of the inner face of the bilayer The rate of transmembrane movement is at least 30,000 times faster than the rate of spontaneous diffusion (flip-flop) of phosphatidylethanolamine across artificial phospholipid bilayers, indicating that transmembrane movement must be a facilitated process in living cells, perhaps involving membrane proteins

Journal ArticleDOI
01 Sep 1977-Nature
TL;DR: In this paper, a detailed study of acyl chain order in the lipids of a natural biological membrane was performed using deuterium NMR of the microorganism Acholeplasma laidlawii.
Abstract: THE most convincing studies of molecular order in model membranes are undoubtedly those involving deuterium nuclear magnetic resonance (NMR) of labelled lipids in the lamellar liquid crystalline phase1–6. The relevance of these results to biological membranes has not yet been established, however; there is no a priori reason to expect the state of organisation of lipids in the lamellar liquid crystal to resemble closely that of a natural membrane. We report here the first detailed study of acyl chain order in the lipids of a natural biological membrane—the plasma membrane of the microorganism Acholeplasma laidlawii. Specifically deuterated fatty acids were incorporated biosynthetically into the membrane lipids as described previously7. The 2H-NMR spectra of the membrane demonstrate the co-existence of at least two different kinds of lipid. Signals from the more fluid lipid are most prominent at temperatures near and above the growth temperature (37 °C). The more solid-like lipid, which predominates at lower temperatures, may be similar to the gel state of lamellar phases and could include lipid associated with the membrane protein. For the more fluid phase, the plot of order parameter against position of deuteration strongly resembles that for egg yolk2 and dipalmitoyl3 phosphatidylcholine. Incorporation of cholesterol into the membrane of A. laidlawii increases the average acyl chain order and also increases the spread of order parameters, similar to its effect on egg yolk phosphatidylcholine6. These results represent a major justification for the use of lamellar liquid crystals as models for the lipid in biological membranes.

Journal ArticleDOI
TL;DR: It is indicated that the increased sphingomyelin/lecithin ratio of acanthocytes is responsible for their decreased membrane fluidity, which occurs coincidentally with an abnormality in cell contour and an impairment in cell deformability.
Abstract: Acanthocytic red cells in patients with abetalipoproteinemia are morphologically similar to the red cells in spur cell anemia. Fluidity of membrane lipids is decreased in spur cells due to their excess cholesterol content. Acanthocyte membranes have an increased content of sphingomyelin and a decreased content of lecithin. To assess the effect of this abnormality of acanthocyte membrane lipid composition on membrane fluidity, we studied red cells from five patients with abetalipoproteinemia and four obligate heterozygote family members. Membrane fluidity was measured in terms of microviscosity (¯η) at 37°C, assessed by means of the fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene. It was increased from 3.2±0.1 poise in normals to 4.01-4.14 poise in acanthocytes. This was associated with an increase in the sphingomyelin/lecithin ratio from 0.84±0.08 in normals in 1.45-1.61 in acanthocytes. The ¯η of acanthocyte membranes was not influenced by the degree of vitamin E deficiency. Similar changes in ¯η were observed in liposomes prepared from red cell lipids. Heterozygotes had normal sphingomyelin/lecithin ratios and normal values for ¯η. The flow activation energy for viscosity, a measure of the degree of order in the hydrophobic portion of the membrane, was decreased from 8.3 kcal/mole in normal red cells to 7.2 kcal/mole in acanthocytes, indicating that acanthocyte membrane lipids are more ordered. Variations in the sphingomyelin/lecithin mole ratio of liposomes prepared from brain sphingomyelin and egg lecithin with equimolar cholesterol caused similar changes in both ¯η and activation energy. The deformability of acanthocytes, assessed by means of filtration through 3-μm filters, was decreased. These studies indicate that the increased sphingomyelin/lecithin ratio of acanthocytes is responsible for their decreased membrane fluidity. As in spur cells and in red cells enriched with cholesterol in vitro, this decrease in membrane fluidity occurs coincidentally with an abnormality in cell contour and an impairment in cell deformability.

Journal ArticleDOI
TL;DR: Radical scavenging experiments indicate that hydroxyl radical attack initiates the oxidative damage, and Dimethyl sulphoxide is exceptional in that it does not protect, but sensitizes, linoleic acid to radiation induced peroxidation.
Abstract: Cellular membranes have been suggested as possible loci for the development of the oxygen effect in radiobiology. Unsaturated lipids from membranes are subject to very efficient radiation-induced peroxidation, and the deleterious effects generally associated with lipid autoxidation could be initiated by ionizing radiation. Oxidative damage in lipids is characterized not only by high yields but also by a profound dose-rate effect. At dose-rates of X-irradiation below 100 rad/min, a very sharp rise occurs in oxidative damage. This damage has been quantified spectrophotometrically in terms of diene conjugation (O.D. 234 mm) and chromatographically in terms of specific 9- and 13-hydroperoxide formation in linoleic acid micelles. Radical scavenging experiments indicate that hydroxyl radical attack initiates the oxidative damage. Dimethyl sulphoxide is exceptional in that it does not protect, but sensitizes, linoleic acid to radiation induced peroxidation. The yields of hydroperoxides are substantial (G=10--40) and can be related to biological changes known to be effected by autoxidizing lipids.

Journal ArticleDOI
TL;DR: A close correlation is shown to exist between the nerve results and those for a phosphaytidylcholine-cholesterol bilayer, suggesting that the site of action of the alkane is in a lipid bilayer region of the nerve mumbrane, which reduces the stability of the ionic channels formed during electrical excitation.

Journal ArticleDOI
TL;DR: The results suggest that phagocytosis is accompanied by a microtubule-dependent reorganization of membrane lipids, indicating that the alteration of microviscosity results at least in part from changes in lipid composition.
Abstract: The effects of phagocytosis on plasma membrane microviscosity were studied by fluorescence depolarization techniques. It was shown that lipophilic probes are accumulated in intracellular vesicles to a significant degree in fibroblasts and neutrophils. Microviscosity was thus determined from the behavior of probes in isolated membranes. Phagocytosis of oil emulsions or polystyrene beads by rabbit polymorphonuclear leukocytes induces a marked decrease in plasma membrane microviscosity that parallels the extent of phagocytosis. Liposomes made from extracts of membrane lipid show qualitatively the same changes, indicating that the alteration of microviscosity results at least in part from changes in lipid composition. The decrease in microviscosity is abolished when colchicine is present during phagocytosis. Addition of colchicine to membranes previously isolated from control or phagocytic cells has no effect on their microviscosity. The results suggest that phagocytosis is accompanied by a microtubule-dependent reorganization of membrane lipids.

Journal ArticleDOI
TL;DR: The adhesion of artificially generated lipid membrane vesicles to Chinese hamster V79 fibroblasts in suspension was used as a model system for studying membrane interactions, and two pathways are suggested-a temperature-sensitive one involving cell surface proteins, and a temperature-independent one.
Abstract: The adhesion of artificially generated lipid membrane vesicles to Chinese hamster V79 fibroblasts in suspension was used as a model system for studying membrane interactions. Below their gel-liquid crystalline phase transition temperature, vesicles comprised of dipalmitoyl lecithin (DPL) or dimyristoyl lecithin (DML) absorbed to the surfaces of EDTA- dissociated cells. These adherent vesicles could not be removed by repeated washings of the treated cells but could be released into the medium by treatment with trypsin. EM autoradiographic studies of cells treated with[(3)H]DML or [(3)H]DPL vesicles showed that most of the radioactive lipids were confined to the cell periphery. Scanning electron microscopy and fluorescence microscopy further confirmed the presence of adherent vesicles at the cell surface. Adhesion of DML or DPL vesicles to EDTA-dissociated cells modified the lactoperoxidase-catalyzed iodination pattern of the cell surface proteins; the inhibition of labeling of two proteins with an approximately 60,000- dalton mol wt was particularly evident. Incubation of cells wit h (3)H-lipid vesicles followed by sodium dodecyl sulfate (SDS)- polyacrylamide gel electrophoresis showed that some of the (3)H-lipid migrated preferentially with these approximately 60,000-mol wt proteins. Studies of the temperature dependence of vesicle uptake and subsequent release by trypsin showed that DML or DPL vesicle adhesion to EDTA- dissociated cells increased with decreasing temperatures. In contrast, cells trypsinized before incubation with vesicles showed practically no temperature dependence of vesicle uptake. These results suggest two pathways for adhesion of lipid vesicles to the cell surface-a temperature-sensitive one involving cell surface proteins, and a temperature-independent one. These findings are discussed in terms of current models for cell-cell interactions.

Journal ArticleDOI
TL;DR: Fluorescence photobleaching recovery and immunofluorescence methods have been used to study the lateral mobility and topographical distribution of a major cell surface glycoprotein (CSP) and suggest that CSP molecules do not interact strongly with other CSP molecule under these conditions.
Abstract: Fluorescence photobleaching recovery and immunofluorescence methods have been used to study the lateral mobility and topographical distribution of a major cell surface glycoprotein (CSP). Both endogenous CSP and fluorescent-labeled exogenous CSP bind to the cell surface in a fibrillar pattern and are immobile on the experimental time scale. Azide, vinblastine, and cytochalasin B do not alter the immobility and cell surface distribution of the CSP molecules. Therefore, oxidative phosphorylation and the cytoskeleton do not seem to be responsible for the properties of the bound glycoprotein. The presence of immobile CSP fibrils does not, however, impede the diffusion of a lipid probe, a ganglioside analogue, or various surface antigens. Therefore, the fibrils apparently do not form a "barrier" across the lipid phase of the plasma membrane. In contrast, concanavalin A binds to CSP and is largely immobile in regions rich in CSP. The presence of immobile concanavalin A receptors in areas or on cells lacking CSP indicates that other types of immobile concanavalin A receptors also exist.CSP does not bind to lipid bilayers composed of phosphatidylcholine or oxidized cholesterol. It does bind to dextran-coated bilayers as a diffuse distribution of mobile molecules that can patch after addition of antibodies to CSP. The latter result suggests that CSP molecules do not interact strongly with other CSP molecules under these conditions. Exogenous CSP binds to regions on the cell surface that already bear CSP. In view of the apparent weakness of CSP-CSP interactions on the lipid bilayer, it seems possible that the assembly of CSP fibrils is nucleated by cell surface components in addition to CSP.

Journal ArticleDOI
TL;DR: Microviscosity (n) of the cell membrane lipid layer was determined in synchronized C1300 mouse neuroblastoma cells (clone Neuro-2A) by fluorescence polarization of 1,6-diphenystratum and imply a direct role of the Cell membrane fluidity in regulation of thecell cycle.
Abstract: Microviscosity (n) of the cell membrane lipid layer was determined in synchronized C1300 mouse neuroblastoma cells (clone Neuro-2A) by fluorescence polarization of 1,6-diphenystratum. The determined n value was maximal in mitosis, decreased markedly in the G1 phase, remained constant at a low level during the S phase, and increased again during the G2 phase. These findings imply a direct role of the cell membrane fluidity in regulation of the cell cycle.

Journal ArticleDOI
TL;DR: It is concluded that lipid exchange through the water phase by way of single molecules or micelles is the mode of communication of these negatively charged lipid vesicles.

Journal ArticleDOI
TL;DR: Pulse Fourier transform proton magnetic resonance techniques have been used to determine the precise location of four membrane fluorescent probe molecules in lipid bilayer model membranes above the gel-to-liquid crystal transition temperature.
Abstract: Pulse Fourier transform proton magnetic resonance techniques have been used to determine (i) the precise location of four membrane fluorescent probe molecules in lipid bilayer model membranes above the gel-to-liquid crystal transition temperature, tm; (ii) the dynamical perturbation of the host lipid molecules induced by incorporation of the probe into the bilayer. The regions of maximal perturbation induced by these probes do not necessarily coincide with their actual location in the bilayer.

Journal ArticleDOI
TL;DR: It is indicated that phospholipid loss is a marker for membrane degradation in rib segments and may be the basis for ethylene synthesis during aging of flower tissue.
Abstract: Rib segments excised from flower buds of Ipomoea tricolor Cav. pass through the same phases of senescence as the respective tissue on the intact plant. Such segments were used to correlate changes in lipid content with known symptoms of aging, such as rolling up of the ribs and ethylene formation. It was found that the level of phospholipid had already started to decline before visible signs of senescence were evident. As the segments began to roll up and to produce ethylene, the rate of phospholipid loss accelerated sharply. During the same period, the level of fatty acids esterified to phospholipids also fell by 40%. No qualitative changes in any lipid component could be detected during senescence. Labeling experiments using 33 P as marker showed that the rate at which radioactivity was lost from phospholipids during aging was parallel to the rate at which the level of total phospholipids declined. Exogenously applied ethylene accelerated the loss of phospholipid and the senescence of rib segments while benzyladenine retarded both of these processes. Ag + , which counteracts the effect of ethylene in many plants, inhibited rolling up of the rib segments but did not affect either spontaneous and ethylene-induced ethylene generation, or phospholipid loss. In contrast, Co 2+ , a purported inhibitor of ethylene synthesis, reduced ethylene production, rolling up, and phospholipid loss. The inhibition of ethylene-induced rolling up by Co 2+ could not be overcome with exogenous ethylene, however. Our results indicate that phospholipid loss is a marker for membrane degradation in rib segments. Changes in membrane integrity and in cellular compartmentation may be the basis for ethylene synthesis during aging of flower tissue.

Journal ArticleDOI
TL;DR: It is concluded that only the glycerophospholipids in the human erythrocyte membrane are involved in the maintenance of the (Ca2+ + Mg2+)-ATPase activity, and in particular that fraction of these phospholipid fraction located in the inner half of the membrane.

Book ChapterDOI
01 Jan 1977
TL;DR: This chapter shall first review the lipid composition of plant biomembranes; then it will be examined where these lipids come from in plant cells, how they are built, and how they integrate the various biomemBRanes or cell organelles.
Abstract: Lipids are important constituents of all biological membranes and play a central role in the molecular organization of these membranes. Structural lipids in plant biomembranes are essentially phospholipids, galactolipids, and sterols. In this chapter we shall first review the lipid composition of plant biomembranes; then we shall examine where these lipids come from in plant cells, how they are built, and how they integrate the various biomembranes or cell organelles. However, membrane lipids have not only a structural role. The activities of many membrane-bound enzymes are controlled by the extent and the quality of the lipid environment within the membranes. The last part of this chapter will deal with the results of some recent studies concerning the effect of lipids upon the activities of some membrane-bound enzymes.

Journal Article
TL;DR: The rationale for and the results of some of the physical chcmistry of the planar bilayer membrane, a particularly rimplc mcmbranc solution consisting of alkane molecules dissolved in a l ipid biloycr, are described.
Abstract: A solution is, by definition, any phase containing trro or more components. Thc ccll membrane is a phasc(6) distirrct from the cytoplasm and interstitium contoining lipids and proteins, and is therefore a solution. Simply calling the membronc a solution, however, provides few new insights into mcmbrane architccture. My luboratory is conccrned vith devcloping quantitative methods for describing thc rolution propcrties of membrane systems that we believe will lead to a deeper undcrstanding of membrane organization. Toward this end, we have been studying thc physical chcmistry ofth€ planar bilayer membrane, rvhich is a particularly rimplc mcmbranc solution consisting of alkane molecules dissolved in a l ipid biloycr. This paper describes the rationale for and the results of some of our crpcrimcnts.

Journal ArticleDOI
TL;DR: The growth-inhibitory activity of two imidazole antimycotics, clotrimazole and miconazole, against Candida albicans was significantly reversed when lipid extracts from protoplast membranes of the same organism were added to the assay medium together with the drugs.
Abstract: The growth-inhibitory activity of two imidazole antimycotics, clotrimazole and miconazole, against Candida albicans was significantly reversed when lipid extracts from protoplast membranes of the same organism were added to the assay medium together with the drugs. Of four major classes of lipids further separated from them, viz., phospholipids, triglycerides, sterol esters, and free sterols, the former two were capable of counteracting both drugs, whereas the latter two were not. However, even with phospholipids or triglycerides, no antagonism was noted when they were saturated by catalytic hydrogenation before use. The antagonistic effect of varying classes of commercial lipids, including phospholipids, acylglycerides, sterols, and fatty acids, was also studied by means of the agar diffusion technique. Significant antagonism to both drugs was observed with: (i) phospholipids with an unsaturated acyl group; (ii) acylglycerides, the ester portion of which consists of unsaturated fatty acid; (iii) ultraviolet-activated sterols; and (iv) unsaturated fatty acids of cis -configuration. By contrast, none of the saturated phospholipids and acylglycerides nor sterols was effective as an antagonist. With the exception only of lauric acid, all of a series of saturated fatty acids and unsaturated trans -fatty acids ranging from C 8 to C 18 in chain length were either minimally effective or completely ineffective. Essentially, there was no qualitative difference between clotrimazole and miconazole in the response to these various lipids.