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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Bioscience reports 11 (1991), S. 387-444 
    ISSN: 1573-4935
    Keywords: chemiosmotic action ; H+ cycle ; Na+ cycle ; coupling ion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The development of membrane bioenergetic studies during the last 25 years has clearly demonstrated the validity of the Mitchellian chemiosmotic H+ cycle concept. The circulation of H+ ions was shown to couple respiration-dependent or light-dependent energy-releasing reactions to ATP formation and performance of other types of membrane-linked work in mitochondria, chloroplasts, some bacteria, tonoplasts, secretory granules and plant and fungal outer cell membranes. A concrete version of the direct chemiosmotic mechanism, in which H+ potential formation is a simple consequence of the chemistry of the energy-releasing reaction, is already proved for the photosynthetic reaction centre complexes. Recent progress in the studies on chemiosmotic systems has made it possible to extend the coupling-ion principle to an ion other than H+. It was found that, in ceertain bacteria, as well as in the outer membrane of the animal cell, Na+ effectively substitutes for H+ as the coupling ion (the chemiosmotic Na+ cycle). A precedent is set when the Na+ cycle appears to be the only mechanism of energy production in the bacterial cell. In the more typical case, however, the H+ and Na+ cycles coexist in one and the same membrane (bacteria) or in two diffeerent membranes of one and the same cell (animals). The sets of $$\Delta \bar \mu H^ + $$ and $$\Delta \bar \mu Na^ + $$ generators as well as $$\Delta \bar \mu H^ + $$ and $$\Delta \bar \mu Na^ + $$ consumers found in different types of biomembranes, are listed and discussed.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Bioscience reports 11 (1991), S. 445-475 
    ISSN: 1573-4935
    Keywords: membrane ; mitochondria ; transport ; chemiosmotics ; ATPase ; channels ; synaptic junctions ; neurotransmitters ; hormones ; P-glycoprotein ; multi-drug resistance ; antibiotics ; ionophores ; oxidative phosphorylation ; cardiac glycosides ; mitochondrial myopathies ; mitochondrial DNA ; ubiquinone ; oxygen radicals ; ageing ; parasites ; diuretics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The concept of chemiosmotic systems arises from the pioneering work of Peter Mitchell on two fronts. One is concerned with the mechanisms by which molecules are transported across membranes which are generally barriers to such transport. These mechanisms are inevitably molecular, and are now yielding their secrets to a combination of structural protein chemistry and molecular biology. The other front is more physiological, and explores the functional relationships between metabolism and transport. Nevertheless, the two fronts form a continuum of mutally related structure and function. Chemiosmotic systems provide a hierarchy of complexity, starting from say a uniporter reconstituted in a chemically defined bilayer, and proceeding to greater complexity in mitochondria, chloroplasts, eukaryotic and prokaryotic cell membranes, and multicellular systems. Their relationship to medicine is profound, because they provide many opportunities for therapeutic intervention. In this paper I present an overview of chemiosmotic systems at different levels of complexity, both molecular and biological, of their involvements in pathology, and of possible pharmacological treatment or prevention of disease.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Bioscience reports 12 (1992), S. 69-76 
    ISSN: 1573-4935
    Keywords: pancreatic islets ; HIT-T15 cells ; 2-ketoisocaproate transport ; metabolism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The transport of the nutrient secretagogue 2-ketoisocaproate (KIC) was studied in isolated rat pancreatic islets and in the HIT-T15 insulinoma cell line using an oil-filtration technique. In both islets and HIT-T15 cells, KIC uptake was a slow process, not reaching equilibrium within 10 min KIC transport was not dependent upon Na+ in the medium, was not inhibited by α-cyano-4-hydroxy-cinnamate nor by 2-amino-2-norborane carboxylic acid (BCH) and did not appear to be electrogenic. Evidence was obtained to suggest that KIC uptake occurred via passive diffusion into the cell of the undissociated acid species. This possibility was supported by the apparent unsaturability of KIC uptake in HIT-T15 cells. Addition of 10–30 mM KIC to dispersed islets cells or HIT-T15 cells produced a rapid intracellular acidification. In islets, the rate of transport of 10 mM KIC was comparable with oxidation rate of the keto-acid suggesting that uptake could be rate-limiting factor for KIC oxidation and thus stimulated insulin release. However, in HIT-T15 cells, the rate of uptake of KIC greatly exceeded the oxidation rate. The low rate of KIC oxidation could explain the poor secretory response of HIT-T15 cells to KIC
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  • 4
    ISSN: 1573-4935
    Keywords: glycosyl phosphatidylinositol ; membrane anchor ; human folate binding proteins ; choroid plexus ; milk and semen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Gel filtration studies in the presence of Triton X-100 showed that treatment with phosphatidylinositol-specific phospholipase C reduced the apparent molecular size of the 100 kDa folate binding protein from human milk, choroid plexus and semen to 25 kDa. Cleavage of a hydrophobic glycosly phosphatidylinositol domain (a membrane anchor) inserting the protein into Triton X-100 micelles could account for this phenomenon.
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  • 5
    ISSN: 1573-4935
    Keywords: Insulin secretion ; pancreatic B-cell ; G-protein ; adenylate cyclase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Rat islets express a pertussis toxin sensitive G-protein involved in receptor-mediated inhibition of insulin secretion. This has been assumed previously to represent “Gi” which couples inhibitory receptors to adenylate cyclase. Incubation of islet G-proteins with32P-NAD and pertussis toxin resulted in the labelling of a band of molecular weight 40,000. This band was very broad and did not allow resolution of individual components. Incubation of the radiolabelled proteins with an anti-Go antiserum resulted in specific immunoprecipitation of a32P-labelled band. These results demonstrate that the complement of pertussis toxin sensitive G-proteins in rat islets includes Go.
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  • 6
    ISSN: 1573-4935
    Keywords: insulin ; phospholipase C ; 5′-nucleotidase ; alkaline phosphatase ; glycosylphosphatidylinositol ; pertussis toxin ; plasma membrane, (rat liver)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Insulin treatment of isolated liver plasma membranes induced the release of 5′-nucleotidase and alkaline phosphatase. This effect was maximal at physiological hormone concentrations, being 36% and 17% for 5′-nucleotidase and alkaline phosphatase respectively, and was fully mimicked by the phosphatidylinositol specific phospholipase C (PI-PLC), thus confirming the presence of a glycosyl-phosphatidylinositol anchoring-system for these exofacial enzymatic proteins. The complete inhibition of insulin dependent enzyme release by neomycin is strongly supportive of an involvement of membrane-located PI-PLC activity. In addition, the insulin-like effect on enzyme release induced by the GTP non-hydrolysable analog, GTP-γ-S, and its sensitivity to the pertussis toxin are in favour of a mediatory role exerted by the G proteins system, in the transduction of some actions of insulin.
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  • 7
    ISSN: 1573-4935
    Keywords: glucocorticoid ; mitogenesis ; receptor ; T-lymphocyte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The treatment of human tonsillar T-lymphocytes with 4-phorbol 12-myristate 13-acetate (PMA), resulted in about two fold increase in glucocorticoid receptor (GR) number, without any significant change in the receptor affinity. This increase disappeared in the presence of cycloheximide. Alone, PMA and calcium inophore A23187 did not affect, but together stimulated, like phytohaemagglutinin (PHA), leucine and, in particular, thymidine incorporation. PMA enhanced slightly the stimulatory effect of PHA. Alone, these agents failed to alter the suppressive effect of dexamethasone on thymidine and leucine incorporation; however, PMA-A23187 and PMA-PHA combinations appeared to antagonize the supression by dexamethasone.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Bioscience reports 12 (1992), S. 109-114 
    ISSN: 1573-4935
    Keywords: energy metabolism ; oxygen consumption ; thymocytes ; ConA
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The influence of ConA on the energy metabolism of quiescent rat thymocytes was investigated by measuring the effects of inhibitors of protein synthesis, proteolysis, RNA/DNA synthesis, Na+K+-ATPase, Ca2+-ATPase and mitochondrial ATP synthesis on respiration. Only about 50% of the coupled oxygen consumption of quiescent thymocytes could be assigned to specific processes using two different media. Under these conditions the oxygen is mainly used to drive mitochondrial proton leak and to provide ATP for protein synthesis and cation transport, whereas oxygen consumption to provide ATP for RNA/DNA synthesis and ATP-dependent proteolysis was not measurable. The mitogen ConA produced a persistent increase in oxygen consumption by about 30% within seconds. After stimulation more than 80% of respiration could be assigned to specific processes. The major oxygen consuming processes of ConA-stimulated thymocytes are mitochondrial proton leak, protein synthesis and Na+K+-ATPase with about 20% each of total oxygen consumption, while Ca2+-ATPase and RNA/DNA synthesis contribute about 10% each. Quiescent thymocytes resemble resting hepatocytes in that most of the oxygen consumption remains unexplained. In contrast, the pattern of energy metabolism in stimulated thymocytes is similar to that described for Ehrlich Ascites tumour cells and splenocytes, which may also be in an activated state. Most of the oxygen consumption is accounted for, so the unexplained process(es) in unstimulated cells shut(s) off on stimulation.
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  • 9
    ISSN: 1573-4935
    Keywords: granulocyte-macrophage colony-stimulating factor ; respiratory burst ; chemiluminescence ; fluorescence activated cell sorting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Neutrophil function and plasma membrane receptor expression was measured in cell suspensions isolated by two separate procedures and in unfractionated whole blood. When cells were prepared by a combined dextran/ficoll procedure, their ability to generate reactive oxidants in response to fMet-Leu-Phe was greater than in corresponding cells isolated by a one-step procedure on Mono-Poly Resolving Medium (M-PRM). Cells prepared by both methods could be primedin vitro by rGM-CSF, but the priming ratio was greater in cells prepared by the latter method. The ability of neutrophils in whole blood to generate reactive oxidants in response to fMet-Leu-Phe was extremely low, but this was increased by more than 10 fold if the blood was pre-incubated with rGM-CSF. Similarly, expression of CD 11b and CD 16 was very low (or undetectable) in neutrophils in whole blood, but this was rapidly increased upon priming. Activation by PMA resulted in a down regulation of CD 16 expression as the receptor was shed from the cell surface. Neutrophils isolated by either the dextran/ficoll or the M-PRM method showed increased expression of receptors compared with those in whole blood, although this expression was lower in cells isolated by the latter method. These data indicate that the isolation procedures used to obtain purified neutrophils prime both receptor expression and oxidase function, although these effects are minimalised in isolation procedures using M-PRM. Furthermore, as CD 16 expression on neutrophils in whole blood is rapidly up-regulated during priming, it seems likely that, as for complement receptors, rapidly-mobilisable intracellular stores of this receptor exist.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Bioscience reports 12 (1992), S. 143-187 
    ISSN: 1573-4935
    Keywords: Fourier transform ; nuclear magnetic resonance ; NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The development and current status of Fourier transform spectroscopy is described.
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