Showing papers on "Membrane published in 1968"

Enzymatic properties of the inner and outer membranes of rat liver mitochondria

Abstract: Treatment of rat liver mitochondria with digitonin followed by differential centrifugation was used to resolve the intramitochondrial localization of both soluble and particulate enzymes. Rat liver mitochondria were separated into three fractions: inner membrane plus matrix, outer membrane, and a soluble fraction containing enzymes localized between the membranes plus some solublized outer membrane. Monoamine oxidase, kynurenine hydroxylase, and rotenone-insensitive NADH-cytochrome c reductase were found primarily in the outer membrane fraction. Succinate-cytochrome c reductase, succinate dehydrogenase, cytochrome oxidase, beta-hydroxybutyrate dehydrogenase, alpha-ketoglutarate dehydrogenase, lipoamide dehydrogenase, NAD- and NADH-isocitrate dehydrogenase, glutamate dehydrogenase, aspartate aminotransferase, and ornithine transcarbamoylase were found in the inner membrane-matrix fraction. Nucleoside diphosphokinase was found in both the outer membrane and soluble fractions; this suggests a dual localization. Adenylate kinase was found entirely in the soluble fraction and was released at a lower digitonin concentration than was the outer membrane; this suggests that this enzyme is localized between the two membranes. The inner membrane-matrix fraction was separated into inner membrane and matrix by treatment with the nonionic detergent Lubrol, and this separation was used as a basis for calculating the relative protein content of the mitochondrial components. The inner membrane-matrix fraction retained a high degree of morphological and biochemical integrity and exhibited a high respiratory rate and respiratory control when assayed in a sucrose-mannitol medium containing EDTA.

Action Potentials induced in Biomolecular Lipid Membranes

Abstract: Alamethicin, a cyclopeptide, can induce action potentials in biomolecular lipid membranes.

Rat intestinal microvillus membranes. Purification and biochemical characterization

Abstract: 1. A technique is described for the removal of subcellular contaminants from intact rat intestinal brush borders, and for the subsequent separation of a microvillus membrane fraction from a fibrillar residue. 2. Increments in invertase activity, microscopic homogeneity and low nucleic acid content indicate that the microvillus plasma membrane has been extensively purified. Multiple membrane preparations have been shown to be highly reproducible with respect to their invertase specific activity, cholesterol content and phospholipid content. Alkaline phosphatase, leucine aminopeptidase, Mg2+- and Ca2+-dependent adenosine triphosphatase and seven separate disaccharidases were shown to be predominantly confined to the membrane fraction. 3. The fibrillar fraction has been shown to contain approximately 30% of the total protein of purified brush borders, plus most of the residual nucleic acid contaminant. No evidence was found for the localization of any specific enzyme in this fraction.

Selective Solubilization of a Protein Component of the Red Cell Membrane

Abstract: Approximately 20 percent of the membrane-bound protein of erythrocyte ghosts can be solubilized and obtained free of other membrane components by dialysis against adenosine triphosphate and 2-mercaptoethanol. This protein forms one major band on polyacrylamide gels and a single boundary in free-boundary electrophoresis, and it undergoes polymerization in the presence of divalent cations to form coiled filaments visible by electron microscopy. Antibodies to this membrane protein react specifically with red blood cells or their membrane ghosts but do not react with serum, erythrocyte cytoplasm, or other blood cells. The functional role of this protein is unknown, but it appears to be involved in maintaiining the structure of the red cell membrane. We suggest that this protein be called Spectrin since it is obtained from membrane ghosts.

Thin Silicone Membranes-Their Permeation Properties and Some Applications

Abstract: While the permeation of gases through solid materials is often a nuisance and sometimes a hazard, in recent years several useful applications have been found for this phenomenon. For example, H, is purified by diffusion through Pd-Ag foils, 0, partial pressures are measured in instruments dependent on 0, permeating through a plastic membrane, and artificial lungs based on permeation of 0, and CO, through thin polymeric membranes are being developed. These applications are only the beginning, for recent advances in membrane technology portend uses as far afield as water desalination by reverse osmosis and the separation of azeotropes by membrane perm-vaporation. When one wishes to separate noncondensable gases by a membrane technique, his first consideration should be whether a silicone rubber membrane can be used. This stems from the unusually high permeability of silicone rubber, indicated in TABLE 1, a tabulation of 0, permeabilities in various membranes.

Membrane Transport Characteristics of Ultrafine Capillaries

Abstract: A detailed study and further development of the capillary model for charged wide‐pore membranes is presented. Previous work on this model has either linearized the Poisson–Boltzmann equation and/or assumed a small Debye length‐to‐tube‐radius ratio, or ignored axial concentration gradients. None of these simplifications are made here. The problem is characterized by a set of nine coefficients coupling the various transport phenomena. We establish these coefficients and combine them to form “figures of merit” which describe the energy conversion capability of the membrane in its various conversion modes. The capillary membrane is found to be considerably more efficient in electrodialysis than in either osmosis or electro‐osmosis.

High flow membrane

Abstract: AN ANISTROPIC HIGH FLUX LOW PRESSURE POLYMERIC MEMBRANE CAPABLE OF BEING DRIED WITHOUT LOSS OF BENEFICIAL MECHANICAL AND PROCESSING CHARACTERISTICS, AND HAVING IN A CONTINUOUS POLYMER PHASE A BARRIER LAYER CONTAINING PORES FROM 1 TO 1000 MILLIMICRONS IN DIAMETER AND AN OPEN POROUS SUPPORT LAYER, THE POLYMER ABSORBING LESS THAN 10 PERCENT MOISTURE AT 100 PERCENT RELATIVE HUMIDITY AT 25*C.

Membranes of animal cells. II. The metabolism and turnover of the surface membrane.

Abstract: Turnover studies of the surface membrane and of cell particulate matter of L cells in tissue culture in logarithmic and plateau phase of growth have been made. The rate of incorporation of isotope into these fractions and the rate of fall of specific activities of labeled L-cell fractions have been observed. The following interpretation of the data appears most likely although other interpretations are possible. Growing and nongrowing cells synthesize approximately similar amounts of surface membrane and particulate material. In the growing cell the material is incorporated with net increases in substance. There is relatively little turnover. In the nongrowing cell newly synthesized material is incorporated, but a corresponding amount of material is eliminated so that there is turnover without net increase of substance. Our results suggest that there is no gross differential turnover between the protein, lipid, and carbohydrate of the surface membrane under the conditions of our experiments. Metabolic inhibitors or omission of amino acids in the culture medium lead to a decrease in synthesis of surface membrane and cell particulates and cause an equivalent decrease in the rate of degradation of surface membrane and of particulates; therefore the synthetic and degradative aspects of turnover appear to be coupled. As cultures of nongrowing cells in suspension or on a glass surface age, their synthetic and turnover capacities diminish. Our results suggest that the cell may exist in a nongrowing state with a level of synthesis similar to that of a growing cell. It can exist in this state with a high level of turnover.

Permeability and Electrical Properties of Thin Lipid Membranes

Abstract: We present and discuss the permeability and electrical properties of thin lipid membranes, and the changes induced in these properties by several agents added to the aqueous phases after the membranes have formed. The unmodified membrane is virtually impermeable to ions and small "hydrophilic" solutes, but relatively permeable to water and "lipophilic" molecules. These properties are consistent with those predicted for a thin film of hydrocarbon through which matter is transported by dissolving in the membrane phase and then diffusing through it. The effect of cholesterol in reducing the water and "lipophilic" solute permeability is attributed to an increase of the "viscosity" of the hydrocarbon region, thus reducing the diffusion coefficient of molecules within this phase. The selective permeability of the membrane to iodide (I-) in the presence of iodine (I2) is attributed to the formation of polyiodides (perhaps I5-), which are presumed to be relatively soluble in the membrane because of their large size, and hence lower surface charge density. Thus, I2 acts as a carrier for I-. The effects of "excitability-inducing material" and the depsipeptides (particularly valinomycin) on ion permeability are reviewed. The effects of the polyene antibiotics (nystatin and amphotericin B) on ion permeability, discussed in greater detail, are the following: (a) membrane conductance increases with the 10th power of nystatin concentration; (b) the membrane is anion-selective but does not discriminate completely between anions and cations; (c) the membrane discriminates among anions on the basis of size; (d) membrane conductance decreases extraordinarily with increasing temperatures. Valinomycin and nystatin form independent conductance pathways in the same membrane, and, in the presence of both, the membrane can be reversibly shifted between a cation and anion permeable state by changes in temperature. It is suggested that nystatin produces pores in the membrane and valinomycin acts as a carrier.

Further characterization of particulate fractions from lysed cell envelopes of halobacterium halobium and isolation of gas vacuole membranes

Abstract: Lysates of cell envelopes from Halobacterium halobium have been separated into four fractions. A soluble, colorless fraction (I) containing protein, hexosamines, and no lipid is apparently derived from the cell wall. A red fraction (II), containing approximately 40 per cent lipid, 60 per cent protein, and a small amount of hexosamines consists of cell membrane disaggregated into fragments of small size. A third fraction (III) of purple color consists of large membrane sheets and has a very similar composition to II, containing the same classes of lipids but no hexosamines; its buoyant density is 1.18 g/ml. The fourth fraction (IV) has a buoyant density of 1.23 g/ml and contains the "intracytoplasmic membranes." These consist mainly of protein, and no lipid can be extracted with chloroform-methanol. Fractions I and II, which result from disaggregation of cell wall and cell membrane during lysis, contain a high proportion of dicarboxyl amino acids; this is in good agreement with the assumption that disruption of the cell envelope upon removal of salt is due to the high charge density. The intracytoplasmic membranes (IV) represent the gas vacuole membranes in the collapsed state. In a number of mutants that have lost the ability to form gas vacuoles, no vacuole membranes or any structure that could be related to them has been found.

Choline acetyltransferase binding to and release from membranes.

Abstract: 1. The binding of non-occluded choline acetyltransferase to synaptosome membranes is a reversible process that is primarily dependent on the pH and ionic strength of the suspending medium. 2. The distribution of soluble enzyme bound to synaptosome membranes was studied by density-gradient centrifuging. 3. Choline acetyltransferase shows enzyme activity both in the free and in the membrane-bound form. 4. Varying the temperature or prolonged hypo-osmotic treatment does not release the membrane-bound enzyme. 5. The release of choline acetyltransferase from membranes by different anions, thiols, adenosine nucleotides and enzyme substrates was studied.

Alteration of the conformation of proteins in red blood cell membranes and in solution by fixatives used in electron microscopy.

Abstract: The effects of several commonly employed fixatives on the three-dimensional conformations of two soluble proteins and the protein of intact red blood cell membranes have been studied by means of circular dichroism measurements in the spectral region of the peptide absorption bands. The fixatives used produced significant and parallel conformational changes in all of the proteins, in the increasing order: glutaraldehyde; OsO4; glutaraldehyde followed by OsO4; and KMnO4. The last two treatments obliterated most of the helical character of the proteins. The significance of these observations to the preparation of specimens for electron microscopy is discussed.

Glycoproteins in membranes.

Abstract: Summary 1. Although the classical models of biomembranes have emphasized the lipid and protein nature of these structures, a small quantity of carbohydrate is present as glycoprotein and glycolipid in animal cell membranes. In this article an attempt has been made to indicate that such carbohydrate materials should be considered in any complete model of animal cell membranes. 2. Various techniques that have demonstrated the presence of glycoproteins in animal cell membranes have been discussed here. In particular, cell electrophoresis, especially when the measurements are combined with specific enzyme treatments of the cells, has indicated that the net negative surface charge on intact viable cells is mainly due to sialic acid-containing glycoproteins and not as previously thought to ionizable phosphate groups associated with a complex phospholipid system. 3. Membrane-bound antigens are complex carbohydrate-containing macro-molecules whose antigenic activity is principally associated with the configuration at terminal positions on the carbohydrate chains. Enzymic degradation of the glycoproteins of the intact plasma membrane of cells, especially erythrocytes, causes profound changes in the immunological behaviour of the cell. 4. Histology and electron microscopy have indicated the presence of carbohydrate at the periphery of many mammalian cells. Some workers consider that such materials are present in a ‘cell coat’ covering the plasma membrane, rather than in the membrane itself. 5. Studies on the isolation and characterization of membrane glycoproteins have indicated that small oligosaccharide units linked to O-seryl or glutamyl residues in proteins are important structural units in plasma membranes. 6. The glycosylation of proteins takes place within the membranes of the endo-plasmic reticulum. Studies of glycoprotein biosynthesis suggest that the cell is able to synthesize a diversity of cell-surface structures from a relatively small number of monosaccharides. 7. Modification of the sialic acid-containing glycoproteins of the plasma membrane affects the transport of materials in and out of cells. Glycoproteins are present in membranes other than the plasma membrane, and are therefore considered to be integral components of membranes; hence the designation ‘cell coat’, whilst useful as a descriptive term, should not be taken to indicate that glycoproteins are constituents of a functional entity separate from that of the membrane. 8. Evidence that membrane glycoproteins may act as sites of interaction between cells is discussed. The involvement of glycoproteins in such a role would explain why the cell had developed a biosynthetic process capable of producing varied surface oligosaccharide structures from monosaccharides.

Subfractionation and composition of microsomal membranes: a review.

Abstract: I. Subfraet toitat lOll of Ifliel’O o11l(P The “pinching off’’ process Henioval of large particles Sedimentation velocity Peinoeabilitv 10115 and 1)H Stability Limitation of tilt i’acent ru ugat l( 01 Separation of rough and smooth no somes Subfractionation of l’otIgh IolicI’sollleS Subfractionatioll of smooth ni iclosolnes Fl’act ionat iOn of submiel’osonlal )art ides Suhfractionat ion of m iclosomal menibral 1(’S Subfract jonation of ho Ulid libosololes Removal of nonmembranous ploteil i II . (‘on l)OSitiOll of’ nli(l’OsOflles

Hexagonal array of subunits in tight junctions separated from isolated rat liver plasma membranes.

Abstract: Solubilization of isolated rat liver plasma membranes in 1% deoxycholate and centrifugation yielded a fraction (pellet) that consisted mainly of tight junctions (zonulae occludentes). An hexagonal array of subunits similar to that previously found in a number of the unfractionated plasma membranes was demonstrated in all the membrane sheets of these preparations by negative staining. It is concluded that the hexagonal subunit pattern is present in the tight junctions, and that this structural differentiation may be related to the intercellular diffusion afforded by the junctional membrane.