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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 13 (1994), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Escherichia coli arginine repressor (ArgR) is an l-arginine-dependent DNA-binding protein that controls expression of the arginine biosynthetic genes and is required as an accessory protein in Xer site-specific recombination at cer and related recombination sites in plasmids. Site-directed mutagenesis was used to isolate two mutants of E. coli ArgR that were defective in arginine binding. Results from in vivo and in vitro experiments demonstrate that these mutants still act as repressors and bind their specific DNA sequences in an arginine-independent manner. Both mutants support Xer site-specific recombination at cer. One of the mutant proteins was purified and shown to bind to its DNA target sequences in vitro with different affinity and as a different molecular species to wild-type ArgR.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. The depressant effects of β-adrenoceptor agonists and phosphodiesterase inhibitors on contractions of slow-contracting mammalian skeletal muscles are associated with increased muscular cyclic AMP levels.2. A strong correlation was found to exist between the percentage depression of contraction and the percentage increase in cyclic AMP level, irrespective of the drug used and regardless of the mechanism of cyclic AMP production.3. The results strongly support the mediatory role of cyclic AMP in the depressant effects of β-adrenoceptor agonists and phosphodiesterase inhibitors on slow-contracting mammalian skeletal muscle contractions.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. The effects of chronic thyroxine treatment on cat soleus muscle contractions were studied.2. Maximum twitch tension, contraction time, half relaxation time and tensiontime integral of maximal twitches of the soleus muscles of thyroxine treated cats were significantly decreased. Consequently, there was a decrease in tension and degree of fusion of incomplete tetanic contractions of the soleus muscle. The maximum tetanic tension was not statistically significantly changed, suggesting that the effects may be due to a decrease in the duration of the active state of the muscle.3. Isoprenaline given intravenously during incomplete tetanic contractions of the soleus muscle caused a statistically significant depression of tension in the control group but not in the thyroxine treated group. This further suggests reduction in the duration of the active state of soleus muscles of thyroxine treated cats.4. Propranolol injected chronically with thyroxine reversed or prevented the depression of tension caused by thyroxine treatment, suggesting the involvement of β-adrenoceptors in these effects.5. The decrease in tension and degree of fusion during incomplete tetanic contractions of the thyroxine treated soleus could be responsible, at least partly, for the muscle weakness and tremor of thyrotoxicosis. Cyclic AMP may possibly be the mediator of these effects.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. Cyclic AMP levels have been determined in the soleus muscles of anaesthetized cats in the absence of drugs, and during depression of incomplete tetanic contractions produced by (-)-isoprenaline, ICI 63,197 (a phosphodiesterase inhibitor) or levodopa.2. Cyclic AMP levels were elevated at the peak of tension depression produced by isoprenaline. Effects of isoprenaline on cyclic AMP and on contractions were dose dependent and statistically significantly related one to the other. Both effects were blocked by propranolol.3. ICI 63,197 and levodopa produced isoprenaline-like effects on contractions but times to peak effect and recovery were longer. Cyclic AMP levels estimated during the depressant action were elevated.4. The results support the involvement of cyclic AMP in the depressant effect of β-adrenoreceptor agonists on slow-contracting mammalian skeletal muscle.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. The effects of 4-methyl-2-thiouracil (MTU, 0.1% in drinking water) on the composition and cross-sectional area of muscle fibres of the rat soleus muscle were studied.2. The percentage of fast twitch-oxidative-glycolytic (FOG) fibres fell after 2 weeks of treatment with MTU to zero at 8 weeks. In contrast the percentage of FOG fibres in untreated animals fell to 19.2±2.1% during this period.3. The mean cross-sectional area of FOG and slow twitch-oxidative (SO) fibres were respectively 39.9% and 23.8% smaller than those of their respective controls 6 weeks after treatment. At 8 weeks the percentage reduction of SO fibre area was 26.8% of the control value.4. This study indicates that MTU treatment causes atrophy and redistribution of fibre type in the soleus muscle.
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. Cyclic AMP and cyclic GMP levels were determined in bovine splenic nerve segments in the absence and presence of (±) - isoprenaline, (-)-phenylephrine, clonidine and ICI 63 197 (a phosphodiesterase inhibitor). The chosen concentrations of adrenoceptor agonists were those which are known to affect stimulation-induced overflow of noradrenaline from nerve terminals.2. The mean levels of cyclic AMP ranged from 229 to 555 pmol/g of microwave irradiated tissue. Mean cyclic GMP levels ranged from 27.9 to 42.2 pmol/g.3.Isoprenaline enhanced cyclic AMP levels but did not affect cyclic GMP levels. The effect was blocked with (±)-propranolol. ICI 63 197 increased cyclic AMP levels but did not change cyclic GMP. Phenylephrine and clonidine caused no consistent changes in cyclic AMP or cyclic GMP levels or in the concentration ratio between these two nucleotides.4.The results support the involvement of cyclic AMP in the enhancing effect of β-adrenoceptor agonists and phosphodiesterase inhibitors on stimulation-induced release of noradrenaline from sympathetic nerves.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. The effects of thyroxine treatment on soleus and extensor digitorum longus (EDL) muscle contractions and their cyclic adenosine 3′,5′-monophosphate (cyclic AMP) levels were examined in anaesthetized cats.2. Thyroxine treatment decreased the tension of incomplete tetanic contractions of the soleus as well as the EDL muscles. The effect on tension of these muscles was not associated with an increase in the cyclic AMP level of the muscle as is the case with a β2-adrenoceptor agonist effect.3. The results do not support the involvement of cyclic AMP in the tension depressant effect of thyroxine on contractions of skeletal muscle.4. It is suggested that the muscle weakness and tremor observed in thyrotoxicosis and during administration of β-adrenoceptor agonists are mediated by different mechanisms.
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  • 8
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. The effects of atropine administration during anticholinesterase poisoning on heart rate, blood pressure and electrocardiographic changes (ECG) were studied in the cat.2. Administration of atropine intravenously during anticholinesterase poisoning caused a significant increase in heart rate and blood pressure; ECG changes were also seen.3. The simultaneous intravenous administration of atropine and labetalol during anticholinesterase poisoning abolished the increase in blood pressure and heart rate; ECG readings remained normal.4. It is suggested that labetalol may be a useful adjuvant in the treatment of anticholinesterase poisoning especially in patients with compromised heart function.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    ISSN: 1440-1681
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: 1. The effects of corticosteroid pretreatment on the contraction caused by acetylcholine or electrical stimulation of guinea-pig ileum and duodenum were studied.2. The acetylcholine dose-response curves for steroid pretreated ileum but not duodenum were significantly shifted to the right; evidence that pretreated ileum required higher dose of acetylcholine than normal to cause 50% maximal contraction.3. Naloxone enhanced the contraction of normal ileum caused by acetylcholine given at the dose of ED50, but not that of normal duodenum.4. The dose of morphine required to abolish electrically induced contraction was higher in steroid pretreated ileum than in normal ileum.5. Hence, corticosteroid pretreatment may affect intestinal contractility via opioidergic mechanisms which are found in the ileum but not in the duodenum.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford UK : Blackwell Science Ltd
    Molecular microbiology 24 (1997), S. 0 
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The Escherichia coli arginine repressor (ArgR) controls expression of the arginine biosynthetic genes and acts as an accessory protein in Xer site-specific recombination at cer and related plasmid recombination sites. The hexameric wild-type protein shows L-arginine-dependent DNA binding. In this work, ArgR mutants that are defective in trimer–trimer interactions and bind DNA as trimers in an L-arginine-independent manner are isolated and characterized. Whereas the wild-type ArgR hexamer exhibits high-affinity binding to two repeated ARG boxes separated by 3 bp (each ARG box containing two identical dyad symmetrical 9 bp half-sites), the trimeric mutants bind to and footprint three adjacent half-sites of this ‘idealized’ substrate. Trimeric ArgR is impaired in its ability to repress the arginine biosynthetic genes and in Xer site-specific recombination. In the absence of L-arginine, residual wild-type ArgR-binding occurs as trimers. The binding of an N-terminal 77-amino-acid DNA-binding domain to idealized ARG boxes is also characterized.
    Type of Medium: Electronic Resource
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