Showing papers on "Membrane published in 1970"
TL;DR: A wide variety of proteins have been shown to bind identical amounts of an amphiphile, sodium dodecyl sulfate, on a gram per gram basis at monomer equilibrium concentrations above 0.5 mM.
Abstract: A wide variety of proteins have been shown to bind identical amounts of an amphiphile, sodium dodecyl sulfate, on a gram per gram basis at monomer equilibrium concentrations above 0.5 mM. The binding is independent of ionic strength and primarily hydrophobic in nature. Only the monomeric form of the amphiphile binds to proteins, not the micellar form. The application of these results to models for biological membranes and to gel electrophoresis in sodium dodecyl sulfate is discussed.
642 citations
TL;DR: In the past 5 years, membrane ultrafiltration has gained increasing prominence as a simple and convenient process for concentrating, purifying, and fractionating solutions of moderate-to-high molecular weight solutes and colloids, and for purifying water and other solvents containing such solutes as discussed by the authors.
Abstract: In the past 5 years, membrane ultrafiltration has gained increasing prominence as a simple and convenient process for concentrating, purifying, and fractionating solutions of moderate-to-high molecular weight solutes and colloids, and for purifying water and other solvents containing such solutes. The emergence of this new molecular separation technique for both laboratory and industrial applications is almost entirely attributable to the development of a family of uniquely structured polymeric membranes which display extraordinarily high hydraulic permeabilities coupled with the capacity to retain even quite small solute molecules.
555 citations
TL;DR: A modified method for the isolation of the plasma membrane from rat liver has been developed and the concentration of Ca2+ and the degree of the homogenizing medium are critical factors in obtaining membranes in high yield and with high activity of the characteristic plasma membrane enzymes.
545 citations
TL;DR: The freeze-etch technique was used to observe red blood cell ghosts labeled on both surfaces with covalently bound ferritin, indicating that fracture does not show membrane-surface detail, and results were consistent with the concept that membranes split during the fracture process of Freeze-etching.
Abstract: The freeze-etch technique was used to observe red blood cell ghosts labeled on both surfaces with covalently bound ferritin. Ferritin molecules were never observed on fracture faces, thus indicating that fracture does not show membrane-surface detail. Subliming away the surrounding ice did expose the ferritin on the membrane surface. These results were consistent with the concept that membranes split during the fracture process of freeze-etching.
517 citations
TL;DR: Membranes prepared from HEp-2 cells infected with herpes simplex virus and free from soluble proteins, virus, ribosomes, and other cellular constituents were solubilized and subjected to electrophoresis on acrylamide gels to show the synthesis of host proteins and glycoproteins ceases after infection.
Abstract: Membranes prepared from HEp-2 cells infected with herpes simplex virus and free from soluble proteins, virus, ribosomes, and other cellular constituents were solubilized and subjected to electrophoresis on acrylamide gels. The electropherograms showed the following. (i) The synthesis of host proteins and glycoproteins ceases after infection. However, the spectrum of host proteins in membranes remains unaltered. (ii) Between 4 and 22 hr postinfection, at least four glycoproteins are synthesized and bound to the smooth cytoplasmic membranes. On electrophoresis, these glycoproteins form two major and two minor bands in the gel and migrate with proteins ranging from 50,000 to 100,000 daltons in molecular weight. (iii) The same glycoproteins are present in all membranes fractionated by density and in partially purified virus. The implications of the data are discussed.
501 citations
TL;DR: Evidence is presented suggesting that nucleotide pyrophosphatase and phosphodiesterase I of rat liver may be manifestations of the same enzyme and the preparative method developed appears to give the best combination of yield, purity, and reproducibility available.
Abstract: Nucleotide pyrophosphatase and phosphodiesterase I of rat liver have been found to be localized primarily in cell particulates highly enriched with respect to the most commonly accepted plasma membrane marker, 5'-nucleotidase, and therefore should themselves be assigned a plasma membrane localization. The observation that plasma membranes sediment in isotonic sucrose with both nuclear and microsomal fractions was exploited to obtain plasma membrane preparations from each fraction. Both preparations are similar in chemical and enzymic composition. Moreover, the preparative method developed in this study appears to give the best combination of yield, purity, and reproducibility available. The question of the possible identity of nucleotide pyrophosphatase and phosphodiesterase I is considered, and evidence is presented suggesting that these activities may be manifestations of the same enzyme.
467 citations
Patent•
Alza1
TL;DR: In this article, a drug-delivery device for releasing drug at a controlled rate for a prolonged period of time is formed from a solid inner matrix material having drug dispersed there through.
Abstract: Drug-delivery device for releasing drug at a controlled rate for a prolonged period of time is formed from a solid inner matrix material having drug dispersed therethrough. Surrounding the inner matrix is an intimately contacting outer polymeric membrane, insoluble in body fluids, which contracts about the matrix as the matrix decreases in volume upon drug release. Both the inner matrix material and the outer polymeric membrane are permeable to passage of the drug by diffusion but the drug diffuses through the outer polymer membrane at a lesser rate so that passage through the polymeric membrane is the drug release rate controlling step. The integrity of the intimate contact between the membrane and the matrix is assured even upon matrix depletion immediately following manufacture and for an extended period of time by reason of the reserve elastic recovery stress in the membrane.
446 citations
TL;DR: The results demonstrate the absence of intracellular membranes and suggest that the outer membrane of the platelet is similar to plasma membranes of other cells, and they provide biochemical confirmation of its origin from the plasma membrane ofThe megakaryocyte.
393 citations
TL;DR: NET ion movements across biological or synthetic lipid membranes may take place by various mechanisms, underlying all of which there is a rather ill-defined and small ion leakage or background conductance.
Abstract: NET ion movements across biological or synthetic lipid membranes may take place by various mechanisms, underlying all of which there is a rather ill-defined and small ion leakage or background conductance. Most ions permeate by means of pathways involving either permanent or transient modifications of the basic structure of the membrane. If permanent pathways are involved, a given membrane conductance may be accounted for by routes which are either numerous and of low conductance or few and of high conductance. For transient pathways, duration must also be considered. Thus, if a carrier is invoked, the duration will be the time the carrier, complexed with an ion, spends shuttling across the membrane. For a pore, the duration is the time for which it remains open to ions. At present little is known concerning the number, conductance and duration of the ionic pathways in any membrane of the types mentioned. Limited information is available for the nerve membrane, although this is rather imprecise and indirect1.
387 citations
TL;DR: A working hypothesis for the fusion of membranes is discussed and it is suggested that the process may involve phase changes in the lipids of membranes with the formation of micellar units of lipid or lipoprotein.
Abstract: A working hypothesis for the fusion of membranes is discussed. It is suggested that the process may involve phase changes in the lipids of membranes with the formation of micellar units of lipid or lipoprotein.
385 citations
TL;DR: Results suggest that the growing end of the nascent polypeptide is resistant to digestion and is protected from proteolytic attack by the ribosomal structure, as suggested by the acrylamide gel electrophoresis pattern.
Abstract: Rough microsomes were incubated in an in vitro amino acid-incorporating system for labeling the nascent polypeptide chains on the membrane-bound ribosomes. Sucrose density gradient analysis showed that ribosomes did not detach from the membranes during incorporation in vitro. Trypsin and chymotrypsin treatment of microsomes at 0° led to the detachment of ribosomes from the membranes; furthermore, trypsin produced the dissociation of released, messenger RNA-free ribosomes into subunits. Electron microscopic observations indicated that the membranes remained as closed vesicles. In contrast to the situation with free polysomes, nascent chains contained in rough microsomes were extensively protected from proteolytic attach. By separating the microsomal membranes from the released subunits after proteolysis, it was found that nascent chains are split into two size classes of fragments when the ribosomes are detached. These were shown by column chromatography on Sephadex G-50 to be: (a) small (39 amino acid residues) ribosome-associated fragments and (b) a mixture of larger membrane-associated fragments excluded from the column. The small fragments correspond to the carboxy-terminal segments which are protected by the large subunits of free polysomes. The larger fragments associated with the microsomal membranes depend for their protection on membrane integrity. These fragments are completely digested if the microsomes are subjected to proteolysis in the presence of detergents. These results indicate that when the nascent polypeptides growing in the large subunits of membrane-bound ribosomes emerge from the ribosomes they enter directly into a close association with the microsomal membrane.
TL;DR: A modification of the freeze-fracturing technique to permit observation of replicas of both sides of the fracture is described, used to study mouse liver cell membrane structure.
Abstract: A modification of the freeze-fracturing technique to permit observation of replicas of both sides of the fracture is described. It has been used to study mouse liver cell membrane structure. Membranes break to give two faces with three-dimensional complementarity, although there is some small-scale mismatching which is discussed. Since the two distinctive sets of membrane faces are complementary sets, they cannot be the two outside surfaces. In particular, structures (such as particles) seen on these faces are within the membrane. It is not possible from this work to say precisely where the fracture plane goes with respect to a plasma membrane, only that it must be close to the interface between membrane and cytoplasm, or at that interface. Models, consistent with the appearance of the matching replicas, are derived for three regions of the plasma membrane: (a) The nonjunctional plasma membrane, which contains many scattered particles. Except for these particles, the otherwise flat fracture face is not at variance with a bimolecular leaflet structure. (b) Gap junctions. Each of the two membranes comprising a gap junction contains a close-packed array of particles. (c) Tight junctions. Here membranes have ridges within them.
TL;DR: Plasma membranes purified from human red cells were Converted into small vesicleS by disruption in alkaline buffer of low ionic strength by centrifugration to equilibrium in dextran density gradients.
Abstract: Plasma membranes purified from human red cells were Converted into small vesicleS by disruption in alkaline buffer of low ionic strength. Most of these vesicles were inside-out. The presence of divalent cations prevented this inversion. The inside-out vesicles were separatcd from right-side-out vesicles by centrifugration to equilibrium in dextran density gradients.
TL;DR: A rapid method of preparing plasma membranes from isolated fat cells is described and electron microscopic evidence suggested contamination of the plasma membrane fraction by other subcellular components to be less than the biochemical data indicated.
Abstract: A rapid method of preparing plasma membranes from isolated fat cells is described. After homogenization of the cells, various fractions were isolated by differential centrifugation and linear gradients. Ficoll gradients were preferred because total preparation time was under 3 hr. The density of the plasma membranes was 1.14 in sucrose. The plasma membrane fraction was virtually uncontaminated by nuclei but contained 10% of the mitochondrial succinic dehydrogenase activity and 25–30% of the RNA and reduced nicotinamide adenine dinucleotide cytochrome c reductase activity of the microsomal fraction. Part of the RNA and NADH-cytochrome c reductase activity was believed to be native to the plasma membrane or to the attached endoplasmic reticulum membranes demonstrated by electron microscopy. The adenyl cyclase activity of the plasma membrane fraction was five times that of Rodbell's "ghost" preparation and retained sensitivity to epinephrine. The plasma membrane ATPase activity was five times that of the homogenate and microsomal fractions. Electron microscopic evidence suggested contamination of the plasma membrane fraction by other subcellular components to be less than the biochemical data indicated.
TL;DR: It is concluded that nystatin and amphotericin B create aqueous pores in thin lipid membranes; the effective radius of these pores is approximately 4 A and there is a marked similarity between the permeability of a nyStatin- or amphoteric in B-treated membrane to water and small hydrophilic solutes and the permeable of the human red cell membrane to these same molecules.
Abstract: Nystatin and amphotericin B increase the permeability of thin (<100 A) lipid membranes to ions, water, and nonelectrolytes. Water and nonelectrolyte permeability increase linearly with membrane conductance (i.e., ion permeability). In the unmodified membrane, the osmotic permeability coefficient, P(f), is equal to the tagged water permeability coefficient, (P(d))(w); in the nystatin- or amphotericin B-treated membrane, P(f)/(P(d))(w) approximately 3. The unmodified membrane is virtually impermeable to small hydrophilic solutes, such as urea, ethylene glycol, and glycerol; the nystatin- or amphotericin B-treated membrane displays a graded permeability to these solutes on the basis of size. This graded permeability is manifest both in the tracer permeabilities, P(d), and in the reflection coefficients, sigma (Table I). The "cutoff" in permeability occurs with molecules about the size of glucose (Stokes-Einstein radius approximate, equals 4 A). We conclude that nystatin and amphotericin B create aqueous pores in thin lipid membranes; the effective radius of these pores is approximately 4 A. There is a marked similarity between the permeability of a nystatin- or amphotericin B-treated membrane to water and small hydrophilic solutes and the permeability of the human red cell membrane to these same molecules.
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.
TL;DR: The effects of polyene antibiotics on thin lipid membranes are consistent with their action on biological membranes, and possibly the many hydroxyl groups in nystatin and amphotericin B are responsible for anion selectivity.
Abstract: Characteristics of nystatin and amphotericin B action on thin (<100 A) lipid membranes are: (a) micromolar amounts increase membrane conductance from 10(-8) to over 10(-2) Omega(-1) cm(-2); (b) such membranes are (non-ideally) anion selective and discriminate among anions on the basis of size; (c) membrane sterol is required for action; (d) antibiotic presence on both sides of membrane strongly favors action; (e) conductance is proportional to a large power of antibiotic concentration; (f) conductance decreases approximately 10(4) times for a 10 degrees C temperature rise; (g) kinetics of antibiotic action are also very temperature sensitive; (h) ion selectivity is pH independent between 3 and 10, but (i) activity is reversibly lost at high pH; (j) methyl ester derivatives are fully active; N-acetyl and N-succinyl derivatives are inactive; (k) current-voltage characteristic is nonlinear when membrane separates nonidentical salt solutions. These characteristics are contrasted with those of valinomycin. Observations (a)-(g) suggest that aggregates of polyene and sterol from opposite sides of the membrane interact to create aqueous pores; these pores are not static, but break up (melt) and reform continuously. Mechanism of anion selectivity is obscure. Observations (h)-(j) suggest-NH(3) (+) is important for activity; it is probably not responsible for selectivity, particularly since four polyene antibiotics, each containing two-NH(3) (+) groups, induce ideal cation selectivity. Possibly the many hydroxyl groups in nystatin and amphotericin B are responsible for anion selectivity. The effects of polyene antibiotics on thin lipid membranes are consistent with their action on biological membranes.
TL;DR: The alveolar membrane represents a tight cellular-type structure, whereas the pulmonary capillary represents a highly permeable, porous structure.
Abstract: TAYLOR, AUBREY E., AND KERMIT A. GAAR, JR. Estimation of equivalent pore radii sf pulmonary capillary and alveolar membranes. Am. J. Physiol. 218(4): 1133-l 140. 1970.-The reflection coefficients (a) of urea, glucose, and sucrose were estimated in an isolated dog lung. The US measured across the capillary for the three test substances were found to be .018 zt .003, .026 =t .002, and .044 ZIZ .004, respectively. The same three test molecules were investigated in fluid-filled lobes and the C’S were calculated to be .59, .72, and .81, respectively, for the alveolar membrane. Also, when flow was varied from fs to 1 ?s times normal no difference was observed in the calculated US for the capillary membrane. Antipyrine produced no osmotic transient across the pulmonary capillary. When (1 a) was plotted as a function of time, a pore radius of 6 10 A was calculated for the alveolar membrane and one of 40 58 A was estimated for the pulmonary capillary membrane. Thus, the alveolar membrane represents a tight cellular-type structure, whereas the pulmonary capillary represents a highly permeable, porous structure.
TL;DR: Inulin penetration occurred at pH 7.0 with 1 mM EDTA and at pH 9.0 without EDTA, suggesting increased permeability of FSR membranes, which accords with the higher rate of Ca++ release from FSR at temperatures over 30°C, and the penetration of microsomal membranes by anions is markedly influenced by charge effects.
Abstract: Fragmented sarcoplasmic reticulum (FSR) membranes isolated from rabbit skeletal muscle are impermeable to inulin-14C (mol wt 5,000), and dextran-14C (mol wt 15,000–90,000) at pH 7.0–9.0, yielding an excluded space of 4–5 µl/mg microsomal protein. In the same pH range urea and sucrose readily penetrate the FSR membrane. EDTA or EGTA (1 mM) increased the permeability of microsomes to inulin-14C or dextran-14C at pH 8–9, parallel with the lowering of the FSR-bound Ca++ content from initial levels of 20 nmoles/mg protein to 1–3 nmoles/mg protein. EGTA was as effective as EDTA, although causing little change in the Mg++ content of FSR. The permeability increase caused by chelating agents results from the combined effects of high pH and cation depletion. As inulin began to penetrate the membrane there was an abrupt fall in the rate of Ca++ uptake and a simultaneous rise in ATPase activity. At 40°C inulin penetration occurred at pH 7.0 with 1 mM EDTA and at pH 9.0 without EDTA, suggesting increased permeability of FSR membranes. This accords with the higher rate of Ca++ release from FSR at temperatures over 30°C. The penetration of microsomal membranes by anions is markedly influenced by charge effects. At low ionic strength and alkaline pH acetate and Cl are partially excluded from microsomes when applied in concentrations not exceeding 1 mM, presumably due to the Donnan effect. Penetration of microsomal water space by acetate and Cl occurs at ionic strengths sufficiently high to minimize charge repulsions.
TL;DR: Detailed comparisons of the lipid composition of Golgi apparatus with those of rough endoplasmic reticulum and plasma membranes are made as a first step in relating morphological differences among these cell components to differences in membrane constituents.
Abstract: Rough endoplasmic reticulum, Golgi apparatus, and plasma membrane rich cell fractions were isolated from livers of rats under similar conditions of age and diet for analysis of phospholipid classes and fatty acid composition. Phosphatidylcholine was the major phospholipid of all membrane types. Golgi apparatus was intermediate between endoplasmic reticulum and plasma membrane with respect to levels of phosphatidylcholine and sphingomyelin. Endoplasmic reticulum was highest in phosphatidylcholine and lowest in sphingomyelin. Levels of lysophosphatidylcholine, phosphatidylserine, phosphatidylinositol, and phosphatidylethanolamine were relatively constant comparing endoplasmic reticulum, Golgi apparatus, and plasma membrane. Lysophosphatidylethanolamine was detected in Golgi apparatus and plasma membrane but not in endoplasmic reticulum. Neutral lipids represented 15 x of the total extractable lipids of endoplasmic reticulum, 38 of the total extractable lipids of plasma membrane, and 46 x of the total extractable lipids of Golgi apparatus. Neutral lipid fractions were composed mainly of cholesterol, free fatty acids, and triglycerides with P recise knowledge on the composition of components comprising the cytoplasmic membrane system of mammalian cells (nuclear envelope, endoplasmic reticulum, Golgi apparatus, secretory vesicles, and plasma membranes) is limited. However, during the last decade development of suitable methods for isolation have permitted detailed characterization of lipids from rat liver plasma membranes (Emmelot et al., 1964; Takeuchi an;d Terayama, 1965; Skipski et al., 1965; Ashworth and Green, 1966; Dod and Grey, 1968; Pfleger et al., 1968) and rough endoplasmic reticulum membranes (Dallner et al., 1966; Glauman and Dallner, 1968). More recently, methods for the reproducible isolation of a highly purified Golgi apparatus fraction of useful quantity have become available (MorrC et al., 1969b), and it is now possible to make detailed comparisons of the lipid composition of Golgi apparatus with those of rough endoplasmic reticulum and plasma membranes as a first step in relating morphological differences among these cell components (Sjostrand, 1963,1968) to differences in membrane constituents. Such comparisons are of importance not only in view of the essential role played by lipids in the structure and function of membranes (Green and Tzagoloff, 1966) but also from the standpoint of clarification of the pro-
TL;DR: Chemical analysis and electron microscopy show that isopycnic centrifugation in discontinuous sucrose density gradients separates smooth and rough cytoplasmic membranes of HeLa cells, and results after addition of guanidine to infected cells support the hypothesis that viral RNA synthesis is initiated in a complex associated with smooth membranes.
TL;DR: It is shown that anions of phenyl dicarbaundecaborane (PCB − ) are extruded from mitochondria on transition to the energized state, and the conclusion is confirmed that it is the electric field (negative inside the mitochondria) which is the motive force for the transport of penetrating ions across the mitochondrial membrane.
TL;DR: X-ray diffraction patterns from dispersions of isolated membranes show that the membrane fatty acyl chains experience a thermal phase transition, and the low angle diffraction indicates that the same general configuration is retained at higher temperatures.
TL;DR: The usefulness of the freeze-etching technique in the study of membranes clearly requires that the controversy over the location of the cleavage plane in membranes be resolved.
Abstract: Freeze-etching promises to be a valuable technique for the ultrastructural study of cells and subcellular components. The tissue specimen is cleaved while frozen by liquid nitrogen, and the exposed faces are replicated by platinum-carbon shadowing while under high vacuum. Thus, this technique eliminates the artifacts of thin-section microscopy produced by fixation, dehydration, embedding, and heavy metal staining. Through the use of this technique, a new feature of cell membrane ultrastructure has been revealed. Cleavage of cell membranes results in the appearance of regularly spaced globular units approximately 85 A in diameter on the exposed membrane face (1, 2). The chemical composition and possible functional properties of the globular units are as yet unknown, and there is also some controversy as to the anatomical location of these structures within the membrane. This controversy is based on a fundamental disagreement as to which face of the membrane is exposed by the cleavage process. Moor and M/ihlethaler (1) and others (3, 4) have suggested that membranes are cleaved along planes which expose either their true outer or cytoplasmic surfaces. According to this view, the 85-A particles are located on the outside surface of the cell membrane; some are also present on the cytoplasmic side of the membrane. It has even been suggested that the particles extend completely through the thickness of the membrane (5). However, studies by Branton (2, 6) question the above interpretations. An analysis of the appearance of membranes in freeze-etched preparations and freeze-cleaving experiments with lipid bilayers has led Branton to conclude that the freeze-fracture process actually splits membranes along a plane within the membrane itself rather than cleaving along its outer or cytoplasmic surface. If this is the case, then the globular particles seen on freeze-cleaved membrane faces would be located somewhere within the interior of the membrane rather than directly on the surface. The usefulness of the freeze-etching technique in the study of membranes clearly requires that the controversy over the location of the cleavage plane in membranes be resolved. One solution would be to label the outer or inner surface of tile membrane with molecules of known structure which can be identified in the freeze-etch prepara-
TL;DR: The intimal relation of cell coats with the plasma membrane, their resistance to physical treatments, and their relation to specific cell types show that they are not merely inert films of condensed ground substance or mucus but integral components of thecell membrane responsible for some of the fundamental properties of the cell surface.
Abstract: Publisher Summary There are two types of surface layers associated with the periphery of animal cells: (1) cell coats, located on the outer surface of most types of cells and (2) basal and external laminas, which border the surface of epithelial and mesenchymal cells, respectively. Both these types of surface layers differ in fine structure, tinctorial affinities, topographical relation to the plasma membrane, and in chemical composition. Cell coats are present in a large variety of animal cells as carbohydrate-containing components of the cell membrane. In some cells, surface coats occur as peripheral sugar moieties of glycoproteins integrated in the plasma membrane and in other cells, they form a thin coat of mucopolysaccharide or glycoprotein material attached to the outer leaflet of the lipoprotein plasma membrane. The intimal relation of cell coats with the plasma membrane, their resistance to physical treatments, and their relation to specific cell types show that they are not merely inert films of condensed ground substance or mucus but integral components of the cell membrane responsible for some of the fundamental properties of the cell surface.