Showing papers on "Membrane published in 1980"

Phospholipid methylation and biological signal transmission

Abstract: Many types of cells methylate phospholipids using two methyltransferase enzymes that are asymmetrically distributed in membranes. As the phospholipids are successively methylated, they are translocated from the inside to the outside of the membrane. When catecholamine neurotransmitters, lectins, immunoglobulins or chemotaxic peptides bind to the cell surface, they stimulate the methyltransferase enzymes and reduce membrane viscosity. The methylation of phospholipids is coupled to Ca2+ influx and the release of arachidonic acid, lysophosphatidylcholine, and prostaglandins. These closely associated biochemical changes facilitate the transmission of many signals through membranes, resulting in the generation of adenosine 3',5'-monophophate in many cell types, release of histamine in mast cells and basophils, mitogenesis in lymphocytes, and chemotaxis in neutrophils.

Lipid conformation in model membranes and biological membranes.

Abstract: Protein molecules in solution or in protein crystals are characterized by rather well-defined structures in which α-helical regions, β-pleated sheets, etc., are the key features. Likewise, the double helix of nucleic acids has almost become the trademark of molecular biology as such. By contrast, the structural analysis of lipids has progressed at a relatively slow pace. The early X-ray diffraction studies by V. Luzzati and others firmly established the fact that the lipids in biological membranes are predominantly organized in bilayer structures (Luzzati, 1968). V. Luzzati was also the first to emphasize the liquid-like conformation of the hydrocarbon chains, similar to that of a liquid paraffin, yet with the average orientation of the chains perpendicular to the lipid–water interface. This liquid–crystalline bilayer is generally observed in lipid–water systems at sufficiently high temperature and water content, as well as in intact biological membranes under physiological conditions (Luzzati & Husson, 1962; Luzzati, 1968; Tardieu, Luzzati & Reman, 1973; Engelman, 1971; Shipley, 1973). In combination with thermodynamic and other spectroscopic observations these investigations culminated in the formulation of the fluid mosaic model of biological membranes (cf. Singer, 1971). However, within the limits of this model the exact nature of lipid conformation and dynamics was immaterial, the lipids were simply pictured as circles with two squiggly lines representing the polar head group and the fatty acyl chains, respectively. No attempt was made to incorporate the well-established chemical structure into this picture. Similarly, membrane proteins were visualized as smooth rotational ellipsoids disregarding the possibility that protruding amino acid side-chains and irregularities of the backbone folding may create a rather rugged protein surface.

Isolation of a heparan sulfate-containing proteoglycan from basement membrane

Abstract: We have isolated a unique, basement membrane proteoglycan from the Engelbreth-Holm-Swarm (EHS) sarcoma. This proteoglycan, estimated to be 0.75 X 10(6) daltons, was found to contain about equal amounts of protein and covalently linked heparan sulfate. Antibody prepared against this proteoglycan reacts with the basement membrane matrix in the tumor and with the basement membranes in skin, kidney, and cornea. These studies indicate that the heparan sulfate proteoglycan is a normal constituent of basement membranes that presumably plays an important role in the organization of basement membrane components and that also may determine the permeability of basement membranes to acidic molecules.

Design of an artificial skin. II. Control of chemical composition.

Abstract: Detailed methodology is described for the reproducible preparation of collagen--glycosaminoglycan (GAG) membranes with known chemical composition. These membranes have been used to cover satisfactorily large experimental full-thickness skin wounds in guinea pigs over the past few years. Such membranes have effectively protected these wounds from infection and fluid loss for over 25 days without rejection and without requiring change or other invasive manipulation. When appropriately designed for the purpose, the membranes have also strongly retarded wound contraction and have become replaced by newly synthesized, stable connective tissue. In our work, purified, fully native collagen from two mammalian sources is precipitated from acid dispersion by addition of chondroitin 6-sulfate. The relative amount of GAG in the coprecipitate varies with the amount of GAG added and with the pH. Since coprecipitated GAG is generally eluted from collagen fibers by physiological fluids, control of the chemical composition of membranes is arrived at by crosslinking the collagen--GAG ionic complex with glutaraldehyde, or, alternately, by use of high-temperature vacuum dehydration. Appropriate use of the crosslinking treatment allows separate study of changes in membrane composition due to elution of GAG by extracellular fluid in animal studies from changes in composition due to enzymatic degradation of the grafted or implanted membrane in these studies. Exhaustive in vitro elution studies extending up to 20 days showed that these crosslinking treatments insolubilize in an apparently permanent manner a fraction of the ionically complexed GAG, although it could not be directly confirmed that glutaraldehyde treatment covalently crosslinks GAG to collagen. By contrast, the available evidence suggests strongly that high-temperature vacuum dehydration leads to formation of chemical bonds between collagen and GAG. Procedures are described for control of insolubilized and "free" GAG in these membranes as well as for control of the molecular weight between crosslinks (Mc). The insolubilized GAG can be controlled in the range 0.5--10 wt. % while "free" GAG can be independently controlled up to at least 25 wt. %; Mc can be controlled in the range 2500--40,000. Studies by infrared spectroscopy have shown that treatment of collagen--GAG membranes by glutaraldehyde or under high-temperature vacuum does not alter the configuration of the collagen triple helix in the membranes. Neither do these treatments modify the native banding pattern of collagen as viewed by electron microscopy. Collagen--GAG membranes appear to be useful as chemically well-characterized, solid macromolecular probes of biomaterial--tissue interactions.

Microbial cell walls and membranes

Abstract: 1 Ultrastructure of bacterial envelopes.- 1.1 Introduction.- 1.2 The Gram-positive cell wall.- 1.3 The Gram-negative cell wall.- 1.4 Membrane morphology.- 1.5 Internal membranes.- 1.6 Specialized membrane systems.- References.- 2 Isolation of walls and membranes.- 2.1 Introduction.- 2.2 Isolation of walls and membranes from Gram-positive species.- 2.3 Separation of the components of the wall from Gram-negative species.- 2.4 Preparation of specialized intracytoplasmic membranes.- References.- 3 Membrane structure and composition in micro-organisms.- 3.1 General ideas of membrane structure.- 3.2 Some physical properties of membranes.- 3.3 Composition of microbial membranes.- 3.4 Proteins in membranes.- References.- 4 Membrane functions.- 4.1 Active components and functions of bacterial cell walls.- 4.2 Functions of the cytoplasmic membrane.- 4.3 Components of the electron transport chain.- 4.4 The coupling of energy flow to phosphorylation.- 4.5 Isolation and properties of Mg2+-Ca2+ ATPase.- 4.6 Vesiculation of membranes.- 4.7 Transport of metabolites and ions.- 4.8 Binding proteins.- 4.9 Mesosomal membrane.- 4.10 Outer membrane of Gram-negative bacteria.- References.- 5 Membranes of bacteria lacking peptidoglycan.- 5.1 Introduction.- 5.2 Mycoplasmas.- 5.3 Extreme halophiles.- 5.4 Bacterial L-forms.- References.- 6 Structure of peptidoglycan.- 6.1 Introduction.- 6.2 Modification of the basic peptidoglycan structure.- 6.3 Three-dimensional structure of peptidoglycans.- 6.4 Cell walls of prokaryotes without peptidoglycan.- References.- 7 Additional polymers in bacterial walls.- 7.1 Gram-positive bacteria.- 7.2 Gram-negative bacteria.- References.- 8 Biosynthesis of peptidoglycan.- 8.1 Introduction.- 8.2 Synthesis of nucleotide sugar precursors.- 8.3 The lipid cycle.- 8.4 Formation of cross-bridge peptides.- 8.5 Polymerization of disaccharide-peptide units.- 8.6 Transpeptidation: The formation of cross-links.- 8.7 D-Alanine carboxypeptidases.- References.- 9 Antibiotics affecting bacterial wall synthesis.- 9.1 Introduction.- 9.2 Phosphonomycin (Fosfomycin).- 9.3 Antibiotics inhibiting D-alanine metabolism in peptidoglycan biosynthesis: cycloserine, O-carbamoyl-D-serine, alaphosphin (L-alanyl-L-1-aminoethyl phosphonic acid) and the haloalanines.- 9.4 Bacitracin.- 9.5 Tunicamycin.- 9.6 The vancomycin group of antibiotics: vancomycin, ristocetins, ristomycins, actinoidin.- 9.7 ?-Lactam antibiotics: the penicillins and cephalosporins.- 9.8 Antibiotics inhibiting biosynthesis of wall polymers but whose site of action is not yet established.- References.- 10 Biosynthesis of other bacterial wall components.- 10.1 Biosynthesis of teichoic acids.- 10.2 Biosynthesis of other components of the Gram-positive bacterial wall.- 10.3 Biosynthesis of the lipopolysaccharides.- 10.4 Iipoprotein from the outer membrane of Gram-negative bacteria.- References.- 11 The bacterial autolysins.- 11.1 Introduction.- 11.2 Bond specificity and distribution of bacterial autolysins.- 11.3 Purification and properties of the autolytic enzymes.- 11.4 Location of autolytic enzymes.- 11.5 Function of autolysins.- References.- 12 Cell walls of Mycobacteria.- 12.1 Wall composition.- 12.2 Adjuvant and other immunostimulant properties.- 12.3 Antitumour activity.- References.- 13 Cell walls of filamentous fungi.- 13.1 Introduction.- 13.2 Carbohydrates in the wall.- 13.3 Wall composition and dimorphism.- 13.4 Melanins and depsipeptides.- 13.5 Conclusion.- References.- 14 Biosynthesis of wall components in yeast and filamentous fungi.- 14.1 Introduction.- 14.2 Biosynthesis of chitin.- 14.3 Biosynthesis of mannan.- 14.4 Biosynthesis of glucan.- References.- 15 The cell wall in the growth and cell division of bacteria.- 15.1 Introduction.- 15.2 Growth of streptococcal cell walls.- 15.3 Growth of the walls of Gram-positive rod-shaped bacteria.- 15.4 Growth of the Gram-negative cell wall.- 15.5 Growth of cytoplasmic membranes.- 15.6 Mutants with disturbed surface growth.- 15.7 Helical growth of bacteria.- References.

Purification of a membrane-associated protein complex required for protein translocation across the endoplasmic reticulum

Abstract: The capacity of microsomal membranes to translocate nascent presecretory proteins across their lipid bilayer can be largely abolished by extracting them with high ionic strength buffers. It can be reconstituted by adding the salt extract back to the depleted membranes [Warren, G. & Doberstein, B. (1978) Nature (London) 273, 569-571]. Utilizing hydrophobic chromatography, we purified to homogeneity a protein component of the salt extract that reconstitutes the translocation activity of the extracted membranes. This component behaves as a homogeneous species upon gel filtration, ion-exchange chromatography, adsorption chromatography, and sucrose-gradient centrifugation. When examined by polyacrylamide gel electrophoresis in NaDodSO4, six polypeptides with apparent Mr of 72,000, 68,000, 54,000, 19,000, 14,000, and 9000 are observed in about equal and constant stoichiometry, suggesting that they are subunits of a complex. The sedimentation coefficient of 11S is in good agreement with the sum of the Mr of the subunits. The Mr 68,000 and 9000 subunits label intensely with N-[3H]ethylmaleimide. Thus, the reported sulfhydryl group requirement of the translocation activity in the unfractionated extract [Jackson, R. C., Walter, P. & Blobel, G. (1980) Nature (London), 286, 174-176] may be localized to either or both the Mr 68,000 and 9000 subunits of the purified complex.

Lipid fluidity markedly modulates the binding of serotonin to mouse brain membranes.

Abstract: The binding of [3H]serotonin to mouse brain crude membrane and synaptosomal membrane preparations was investigated as a function of membrane fluidity changes by lipids. The microviscosity (eta) of the synaptic membranes was increased by in vitro incubation with either cholesteryl hemisuccinate or stearic acid, resulting in an up to 5-fold increase in the specific binding of [3H]serotonin. Serotonin binding increased progressively until it reached a maximum at 1.75 relative eta units; then it declined. Fluidization of membrane lipids, by treatment with lecithin or linoleic acid, caused a small but significant decrease in serotonin binding. These observations are compatible with the concept of vertical displacement of membrane proteins, indicating that in the untreated brain tissue the accessibility (Bmax) of serotonin receptor binding sites constitutes only a fraction (about 20%) of the potential binding capacity stored in the membrane. Scatchard plots of [3H]serotonin binding, at different eta values, indicate a continuous change in the binding affinity (Kd) of serotonin to its receptor, concomitant with changes in its accessibility. These results may have important implications for physiological processes in the central nervous system, which are associated with modulation of membrane lipids, such as aging. In addition, the regional heterogeneity and plasticity of receptors may be accounted for by differences in membrane lipid fluidity. It was found here that various brain regions differ markedly in their membrane lipid viscosity.

Introduction to biological membranes

Abstract: Components of Biological Membranes Self- Association of Phospholipids Properties of Bilayers Order and Dynamics in Bilayers Solutes in Bilayers Lipid-Protein Interactions in Membranes Glycoproteins and Glycolipids Ionophores: Models for Channels and Carriers Facilitated Transport Coupled Transport Gated Channels Energy Transduction Transbilayer Response of Signals Bulk Transport by Fusion and Secretion.

Secretion and Membrane Localization of Proteins in Escherichia Coli

Abstract: The envelope of Escherichia coli consists of two distinct membranes, the outer membrane and the cytoplasmic membrane. The space between the two membranes is called the periplasmic space, and each fraction contains its own specific proteins. In this review, it is discussed how proteins are localized in their final locations in the envelope. Proteins localized in the outer membrane and the periplasmic space as well as transmembranous proteins in the cytoplasmic membranes appear to be produced from their precursors which have peptide extensions of about 20 amino acid residues at the amino terminal ends. General features for the peptide extension are deduced from the known sequences of the peptide extensions, and, based on their known properties, a hypothesis (loop model) is proposed to explain the possible functions of the peptide extension during the mechanism of secretion across the cytoplasmic membrane.

Design of an artificial skin. Part III. Control of pore structure.

Abstract: Several methods are compared for preparing collagen-glycosaminoglycan (GAG) membranes of high or low porosity. Collagen-GAG membranes have been used to cover satisfactorily large experimental full-thickness skin wounds in guinea pigs over the past few years. Methods studied as means for controlling pore size are confined to purely physical processes which do not require use of additives or chemical reagents to form the porous membrane. We find that membranes, initially swollen in distilled water or saline, shrink linearly to no less than 94% of original dimension after freeze drying; to 75% after critical point drying (from CO2, following water-ethanol exchange); and to 41% of original dimension following air drying from the swollen state. Scanning electron microscopic study of the pore structure resulting from eah drying procedure confirms our major conclusion: A carefully designed freeze drying process, two variants of which are described in detail, yields membranes with the highest mean pore size, as measured by quantitative stereological procedures. Critical point drying gave significantly more shrinkage and a lower mean pore size than either one of the two freeze drying procedures used.

Process for preparing liquophilic polyamide membrane filter media and product

Abstract: A process is provided for preparing skinless hydrophilic alcohol-insoluble polyamide membranes by preparing a solution in a polyamide solvent of an alcohol-insoluble polyamide resin having a ratio CH 2 :NHCO of methylene CH 2 to amide NHCO groups within the range from about 5:1 to about 7:1 inducing nucleation of the solution by controlled addition to the solution of a nonsolvent for the polyamide resin, under controlled conditions of concentration, temperature, addition rate, and degree of agitation to obtain a visible precipitate of polyamide resin particles which may or may not thereafter partially or completely redissolve, thereby forming a casting solution; spreading the casting solution on a substrate to form a thin film thereof on the substrate; contacting and diluting the film of casting solution with a mixture of solvent and nonsolvent liquids containing a substantial proportion of the solvent liquid, but less than the proportion in the casting solution, thereby precipitating polyamide resin from the casting solution in the form of a thin skinless hydrophilic membrane; and washing and drying the resulting membrane; the alcohol-insoluble polyamide membranes obtained by this process have the unusual property of being hydrophilic, i.e., readily wetted by water, have absolute particle removal capabilities of the order of 0.1 to 5 μM or more, and are useful as filter media, particularly for producing bacterially sterile filtrates.

The mechanism of protein secretion across membranes

Abstract: Many secreted proteins are synthesised as a large precursor with an additional hydrophobic N-terminal signal sequence that is cleaved by a membrane-bound enzyme. The proteins are secreted as nascent chains. The work leading to the current models of protein secretion is reviewed and the value of bacterial systems in the study of protein transfer across membranes is stressed.

Studies of Schwann cell proliferation. II. Characterization of the stimulation and specificity of the response to a neurite membrane fraction.

Abstract: When prepared by methods utilized in our laboratory, pure populations of Schwann cells in culture do not divide, but, after recombination with peripheral sensory neurons or their processes, proliferate rapidly (Wood and Bunge, 1975, Nature (Lond.) 256:661--664). In this paper, we demonstrate that a membrane fraction prepared from sensory ganglion neurites is also mitogenic for Schwann cells and increases the labeling index (assessed by autoradiography after incubation of cells with tritiated thymidine) from less than 0.2 to 10% for primary cells, and from 0.4 to 18--19% for replated cells. The increased responsiveness of replated cells may reflect their greater access to the neurite membranes which is a consequence of the elimination of multiple cell layers after replating and the removal of the basal lamina. This stimulation was specific; addition of membrane preparations from other cell types (3T3, C1300, etc.) was not mitogenic. Ultrastructural analysis demonstrated apparent binding of neurite membranes to Schwann cells as well as significant phagocytosis of the membranes by the cells. The uptake of nonmitogenic membranes suggests that phagocytosis per se is not the stimulus of proliferation.

The use of isolated membrane vesicles to study epithelial transport processes.

Abstract: Epithelia are multicompartment and multicomponent systems performing transcellular and paracellular transport in a very complex manner. One way to get a deeper understanding of the function of such a complex system is to dissect it into the single components and then, after having defined the components under well-controlled conditions, to try to describe the behavior of the whole system on the basis of the properties of the single components. This article deals with the analysis of isolated plasma membranes derived from the luminal and contraluminal face of epithelial cells, predominantly renal proximal tubular and small intestinal cells. It is aimed to give an overview of methods used to isolate and separate plasma membranes, to study their transport properties as membrane vesicles, and also to address the question of how information gained with the isolated membranes corresponds to observations made in the intact cell using other, notably electrophysiological, measurements. The review also critically evaluates the limitations of the approach and thereby tries to set the work on isolated membranes in the proper perspective within the field of transport physiology.

Assembly of proteins into membranes

Abstract: Two pathways for protein assembly into biological membranes have been proposed. The "signal hypothesis" emphasizes the role of specific membrane proteins in binding the growing polypeptide and conducting it into the bilayer during its synthesis. The "membrane-triggered folding" hypothesis emphasizes self-assembly and the role of changing protein conformation during transfer from an aqueous compartment into a membrane. These ideas provide a framework for reviewing recent data on the biogenesis of membrane proteins.