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  • emulsion polymerization  (3)
  • Sulfate reducers  (2)
  • [3H]Acetylcholine release  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Effects of nicotine receptor agonists on acetylcholine release from the isolated motor nerve, small intestine and trachea of rats and guinea-pigs (1992)
    Springer
    Journal of molecular medicine 70 (1992), S. 182-189 
    Details
    ISSN: 1432-1440
    Keywords: Motor nerve ; Intestine ; Airways ; Neuronal nicotine receptors ; Muscular nicotine receptors ; Receptor desensitization ; [3H]Acetylcholine release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of nicotine receptor agonists on the release of [3H]acetylcholine from the phrenic nerve, the small intestine and the trachea were investigated to characterize neuronal nicotine receptors within the peripheral nervous system. Contraction of the indirectly-stimulated hemidiaphragm was recorded to investigate desensitization of the postsynaptic muscular nicotine receptors. Nicotine, cytisine, 1,1-dimethyl-4-phenylpiperazinium and 2-(4-aminophenyl)-ethyl-trimethyl-ammoniumiodide caused a concentration-dependent (0.1–30 μM) increase in evoked [3H]acetylcholine release from the phrenic nerve, whereby bell-shaped concentration-response curves were obtained. The rank order of decreasing potency was: nicotine 〉 cytisine 〉 1,1-dimethyl-4-phenylpiperazinium 〉 2-(4-aminophenyl)-ethyl-trimethyl-ammoniumiodide. The presynaptic effects of nicotine depended strongly on the exposure time: facilitation occurred after a short 20 s exposure and inhibition after a 3 min exposure, whereas nicotine no longer affected evoked [3H]acetylcholine release after a 15 min exposure. Pre-exposure (40 min) of the phrenic nerve to 0.3 μM nicotine prevented any subsequent modulatory effect of a high nicotine concentration. In contrast, the contraction of the indirectly-stimulated hemidiaphragm remained unaffected in the presence of 0.3–30 μM nicotine, but a concentration of 1 mM nicotine abolished skeletal muscle contraction. Nicotine (10 μM) produced a substantial release of [3H]acetylcholine in the small intestine but not in the isolated trachea. The present experiments show presynaptic nicotine receptors at the phrenic nerve, which, under appropriate conditions, can mediate facilitation of evoked transmitter release. These neuronal receptors appear more sensitive to desensitizing conditions than the postsynaptic muscular nicotine receptors. Nicotine also mediates a transient release of acetylcholine in the myenteric plexus but not in the trachea, and as a consequence, applied nicotine preferentially activates smooth muscle activity in the intestine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00184649
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  • 2
    Electronic Resource
    Electronic Resource
    Formylmethanofuran: tetrahydromethanopterin formyltransferase and N 5,N 10-methylenetetrahydromethanopterin dehydrogenase from the sulfate-reducing Archaeoglobus fulgidus: similarities with the enzymes from methanogenic Archaea (1993)
    Springer
    Archives of microbiology 159 (1993), S. 225-232 
    Details
    ISSN: 1432-072X
    Keywords: Archaea ; Methanogens ; Sulfate reducers ; Tetrahydromethanopterin ; Methanofuran ; Coenzyme F420 ; C1-Enzymes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The sulfate-reducing Archaeoglobus fulgidus contains a number of enzymes previously thought to be unique for methanogenic Archaea. The purification and properties of two of these enzymes, of formylmethanofuran: tetrahydromethanopterin formyltransferase and of N 5,N 10-methylenetetrahydromethanopterin dehydrogenase (coenzyme F420 dependent) are described here. A comparison of the N-terminal amino acid sequences and of other molecular properties with those of the respective enzymes from three methanogenic Archaea revealed a high degree of similarity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00248476
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  • 3
    Electronic Resource
    Electronic Resource
    N 5,N 10-Methenyltetrahydromethanopterin cyclohydrolase from the extremely thermophilic sulfate reducing Archaeoglobus fulgidus: comparison of its properties with those of the cyclohydrolase from the extremely thermophilic Methanopyrus kandleri (1993)
    Springer
    Archives of microbiology 159 (1993), S. 213-219 
    Details
    ISSN: 1432-072X
    Keywords: Archaea ; Methanogenic bacteria ; Hyperthermophiles ; Sulfate reducers ; Methanobacterium thermoautotrophicum ; Methanosarcina barkeri ; Tetrahydromethanopterin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Archaeoglobus fulgidus and Methanopyrus kandleri are both extremely thermophilic Archaea with a growth temperature optimum at 83°C and 98°C, respectively. Both Archaea contain an active N 5,N 10-methenyltetrahydromethanopterin cyclohydrolase. The enzyme from M. kandleri has recently been characterized. We describe here the purification and properties of the enzyme from A. fulgidus. The cyclohydrolase from A. fulgidus was purified 180-fold to apparent homogeneity and its properties were compared with those recently published for the cyclohydrolase from M. kandleri. The two cytoplasmic enzymes were found to have very similar molecular and catalytic properties. They differed, however, significantly with respect of the effect of K2HPO4 and of other salts on the activity and the stability. The cyclohydrolase from A. fulgidus required relatively high concentrations of K2HPO4 (1 M) for optimal thermostability at 90°C but did not require salts for activity. Vice versa, the enzyme from M. kandleri was dependent on high K2HPO4 concentrations (1.5 M) for optimal activity but not for thermostability. Thus the activity and structural stability of the two thermophilic enzymes depend in a completely different way on the concentration of inorganic salts. The molecular basis for these differences are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00248474
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  • 4
    Electronic Resource
    Electronic Resource
    Release of [3H]acetylcholine from the isolated rat or guinea-pig trachea evoked by preganglionic nerve stimulation; a comparison with transmural stimulation (1991)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 344 (1991), S. 403-411 
    Details
    ISSN: 1432-1912
    Keywords: Isolated trachea ; Preganglionic stimulation ; Transmural stimulation ; [3H]Acetylcholine release ; [3H]Phosphorylcholine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Basal and stimulated outflow of radioactive acetylcholine, phosphorylcholine and choline from rat and guinea-pig isolated tracheae were measured by reverse phase HPLC followed by liquid-scintillation-spectrometry. Tracheae were stimulated either by an electrical field (transmural stimulation) or by a local stimulation of the innervating parasympathetic nerves (preganglionic stimulation). Epithelium was removed in most experiments, as the epithelium inhibits acetylcholine release. The basal tritium efflux (1,600 dpm/3min) from rat isolated tracheae incubated with [3H]choline consisted of 56% [3H]phosphorylcholine and 38% [3H]choline. Preganglionic stimulation (15 Hz, 1,200 pulses) caused a 2-fold increase in tritium outflow that was abolished by the removal of extracellular calcium or by the addition of tetrodotoxin. The stimulated outflow of tritium induced by preganglionic nerve stimulation was caused by an exclusive release of [3H]acetylcholine, whereas the efflux of [3H]phosphorylcholine and [3H]choline remained unaffected by this stimulation mode. Transmural stimulation of the rat or guinea-pig trachea, however, caused, in addition to the release of [3H]acetylcholine, the outflow of [3H]phosphorylcholine. Hexamethonium (300 μmol/l) or tubocurarine (100 μmol/l) inhibited (80%) the increase in tritium outflow evoked by preganglionic stimulation, but did not affect tritium outflow evoked by transmural stimulation. Oxotremorine reduced [3H]acetylcholine release evoked by both stimulation modes, but oxotremorine was less potent with transmural stimulation. Scopolamine (0.3 μmol/l) enhanced (120%) the release of [3H]acetylcholine evoked by preganglionic nerve stimulation indicating the blockade of an endogenous negative muscarinic feedback mechanism. Epithelium-dependent inhibition of [3H]acetylcholine release was evident with both preganglionic and transmural stimulation. The present experiments demonstrate the release of [3H]acetylcholine evoked from the isolated trachea by stimulation of the preganglionic trunk of the parasympathetic cholinergic nerves. Qualitative and quantitative differences were observed in comparison to transmural stimulation. Preganglionic nerve stimulation allows a selective excitation of pulmonary, parasympathetic nerve fibres, mimics the physiological excitation of intramural neurones and is not followed by the liberation of phosphorylcholine from non-neuronal cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00172579
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  • 5
    Electronic Resource
    Electronic Resource
    Details of the emulsion polymerization of styrene using a reaction calorimeter (1996)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 34 (1996), S. 461-473 
    Details
    ISSN: 0887-624X
    Keywords: calorimetry ; styrene ; kinetics ; emulsion polymerization ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An automated reaction calorimeter was used to directly monitor the rate of emulsion polymerization of styrene using different emulsifier (sodium lauryl sulfate) and initiator (potassium persulfate) concentrations. By using this technique in conjunction with off-line measurements of the evolution of the particle size distributions, important details of the process were observed. The classical constant rate period (Interval II) often reported for the batch emulsion polymerization of styrene was not seen in this work. Instead, the experimental results suggest that the end of nucleation and the disappearance of monomer droplets take place at approximately the same conversion (36-40%). From the polymerization rate data, important parameters such as the monomer concentration in the polymer particles and the average number of radicals per particle were calculated. © 1996 John Wiley & Sons, Inc.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Role of the nonionic surfactant Triton X-405 in emulsion polymerization. I. Homopolymerization of styrene (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 3813-3825 
    Details
    ISSN: 0887-624X
    Keywords: reaction calorimetry ; emulsion polymerization ; kinetics ; styrene ; nonionic surfactant ; Triton X-405 ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The emulsion polymerization of styrene was studied using the nonionic surfactant Triton X-405 (octylphenoxy polyethoxy ethanol). Two separate nucleation periods were noted in these polymerizations resulting in bimodal final latex particle size distributions. The partitioning of the surfactant between the phases was found to play the major role in determining the nucleation mechanism(s) in these polymerizations. Although the total concentration of the emulsifier was always added at a level above its critical micelle concentration (CMC) based on the water phase in the recipe, it was found that the portion of the surfactant initially present in the aqueous phase was below its CMC due to the partitioning. This CMC was also found to increase with increasing total surfactant because the distribution of the surfactant (varying ethylene oxide chain length) depended on the partitioning between the phases. Under these conditions, the first of the two nucleation periods was attributed to homogeneous nucleation, while the second was attributed to micellar nucleation. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3813-3825, 1997
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Role of the nonionic surfactant Triton X-405 in emulsion polymerization. II. Homopolymerization of n-butyl acrylate (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part A: Polymer Chemistry 35 (1997), S. 3827-3835 
    Details
    ISSN: 0887-624X
    Keywords: reaction calorimetry ; emulsion polymerization ; n-butyl acrylate ; nonionic surfactant ; Triton X-405 ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the emulsion polymerization of n-butyl acrylate, the nonionic surfactant Triton X-405 (octylphenoxy polyethoxy ethanol) partitions primarily into the aqueous phase leading to nucleation in the presence of micelles and unimodal final latex particle size distributions. Nucleation is accompanied by limited aggregation in the early stages of the reactions with particles being formed in some cases past 50% conversion depending on the experimental conditions. High values of the average number of radicals per particle (n̄ 〉 10) are observed during these reactions which explains a secondary increase in the heat of reaction. This increase was not observed when the initiator (K2S2O8) concentration was reduced from 6.4 to 0.6 mM or the temperature was decreased from 70°C to 60°C; contrary to what was expected, an inverse relationship was observed between the rate of polymerization and the final number of particles for these experiments. This was attributed to more extensive limited aggregation at the higher temperature and initiator concentration. Limited aggregation is thus shown to be an important mechanism in these polymerizations. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3827-3835, 1997
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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