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  • 1
    ISSN: 0303-7207
    Keywords: (Rat) ; (Suckling) ; Pituitary ; Prolactin ; Tubulin
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1365-2826
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: In order to evaluate the role of guanine nucleotide-dependent transducer proteins (G proteins) in hormone-mediated signal transduction in the anterior pituitary lobe, we examined the effect of gonadotropin-releasing hormone (GnRH) and thyrotropin-releasing hormone (TRH) on two parameters of G protein function, namely [35 S]GTPγS binding and low KmGTPase activity. Plasma membranes were prepared from anterior pituitary lobes of adult male rats using conventional procedures. GTP binding was determined by incubating 2 to 5 μg membrane protein with approximately 100,000 cpm [35 S]GTPγS in a buffer containing 20 mM Tris- HCl, 1 mM EDTA, 1 mM dithiothreitol, and 100 mM NaCI at a pH of 7.4 for 10 or 15 min at 37 °C GnRH agonist and TRH stimulated high affinity [35 S]GTPγS binding in a concentration-dependent manner. GTP binding was maximally stimulated by GnRH agonist (1 μM) and TRH (0.1 μM) by up to 27% and 34%, respectively. A time-course study revealed that 1 μM GnRH agonist stimulated GTP binding by 30% at 15 min; 0.1 μM TRH stimulated GTP binding by 23% at 1 min, 18% at 5 min and 25% at 10 min. A stable GTP analog, 5′-guanylylimidodiphosphate, inhibited GnRH- as well as TRH-stimulated GTP binding. GnRH antagonist did not affect GTP binding. However, in the presence of the antagonist, stimulation of GTP binding by the GnRH agonist was completely blocked.The low KmGTPase activity (EC 3.6.1.-), another parameter of G protein function, was assayed in 2 to 5 μg membrane protein using [γ-32 P]GTP at 37 °C in an ATP-regenerating buffer containing 1 μM unlabeled GTP. GnRH agonist (0.1 μM) and TRH (1 μM) maximally stimulated this GTPase activity by up to 50% and 40%, respectively. GnRH agonist (1 μM) stimulated the GTPase activity by 30% at 10 min and 48% at 30 min. TRH (1 μM) stimulated the GTPase activity at all time points monitored; stimulation was 46% at 5 min, 49% at 20 min, and 41% at 30 min. Interestingly, the GnRH antagonist stimulated GTPase activity by about 20%, but inhibited GnRH agonist-stimulated GTPase activity in a concentration-dependent manner. These results indicate that the binding of GnRH and TRH to their receptors results in interaction of the receptor with a G protein and activation of the G protein cycle.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 16 (1974), S. 257-258 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The paper reports a possible allelopathic potential of Aristida adscensionis Linn. on the nodulation of Indigofera cordifolia Heyne ex. Roth., at Rajkot (India). When individual plants of I. cordifolia were excavated from plots where it grows in association with A. adscensionis and where A. adscensionis is absent and the nodule numbers counted, it has been observed that the number of nodules was fewer in plants when it grows in association with A. adscensionis. Statistical analysis of the results has confirmed that the standard error of difference in means is highly significant at 1% probability level. Hence it appears that A. adscensionis has some inhibitory effect on the nodulation of I. cordifolia through some mechanism which is yet to be determined. Further work in this direction is in progress.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0730-2312
    Keywords: G proteins ; cytoskeleton ; pituitary cells ; signal transduction ; prolactin ; thyrotropin-releasing hormone ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: In order to study Gq-tubulin interaction in the cytosol, GH3 and AtT-20 cells (stably expressing TRH receptor) were transiently transfected with Gqα cDNA. Forty-eight hours after transfection, thyrotropin-releasing hormone (TRH)-stimulated prolactin (PRL) secretion by Gqα-transfected GH3 cells increased by 90% compared to mock-transfected cells. In addition, using immunocytochemistry it was observed that Gqα-specific staining was much more prominent in Gqα-transfected GH3 and AtT-20 cells (also transfected with Gqα) compared to mock-transfected cells. Thus, transfection resulted in successful overexpression of functional Gqα. Forty-eight hours after transfection, cells were processed to obtain soluble and polymerized tubulin fractions. Tubulin levels were determined in these fractions by immunoblotting using polyclonal anti-tubulin antibodies. Compared to mock-transfected cells soluble tubulin levels decreased in Gqα-transfected GH1 and AtT-20 cells, by 33 and 52%, respectively. Moreover, compared to mock-transfected cells a 50% reduction in the ratio (an index of the flux between tubulin pools) of soluble and polymerized tubulin levels was observed in Gqα-transfected GH3 and AtT-20 cells. To determine whether these effects on tubulin were mediated by Gq directly, we examined the influence of purified Gq on tubulin polymerization. Gq (0.5 μM) inhibited polymerization of crude tubulin (present in GH3 cell cytosol) by 53%. In contrast to its effects on GH3 cell cytosol tubulin, Gq stimulated purified tubulin polymerization by 160%. These results suggest that Gq modulates the polymerization and depolymerization cycles of tubulin and that this modulation is in turn influenced by other unknown cellular components. © 1996 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 53 (1993), S. 181-189 
    ISSN: 0730-2312
    Keywords: G proteins ; liver ; insulin ; rat ; human ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Plasma membranes (1-2 mg protein) prepared from the livers of adult male rats and human organ donors were incubated with 0.6 μM [α-32P] guanosine triphosphate (GTP) in an adenosine triphosphate (ATP)-regenerating buffer at 37°C for 1 h; during this incubation, the [32P]GTP is hydrolyzed and the nucleotide that is predominantly bound to the membranes is [32P] guanosine diphosphate (GDP). [32P]GDP release from the liver membranes was proportional to the protein concentration and increased as a function of time. At 5 mM, Ca2+, Mg2+, Mn2+, and Zn2+ maximally inhibited GDP release by 80-90%, whereas, 5 mM Cu2+ maximally stimulated the reaction by 100%. Therefore, cations were not included in the buffer used in the GDP release step. One μM Gpp(NH)p (5′-guanylylimidodiphosphate), a nonhydrolyzable analog of GTP, maximally stimulated [32P]GDP release in the liver membranes by up to 30%. Although 10 nM Gpp(NH)p had no effect on GDP release, it appeared to stabilize the hormonal effect by blocking further GDP/GTP exchange.In the rat membranes, 1-100 nM glucagon (used as a positive control) stimulated [32P]GDP release by about 17% (P 〈 .05); similarly, 0.1-100 nM insulin stimulated [32P]GDP release by 10-13% (P 〈 .05). In the human membranes, 10 pM to 100 nM insulin stimulated [32P]GDP release by 7-10%. In the rat membranes, 10 nM insulin stimulated [32P]GDP release by 17 and 24% at 2 and 4 min, respectively (P 〈 .05); in the human membranes, 10 nM insulin stimulated [32P]GDP release by about 9% at 2 and 4 min. Normal rabbit IgG (used as a control for insulin receptor antibody) by itself stimulated the GDP release by rat and human membranes. However, the stimulation of the GDP release by insulin receptor antibody was consistently higher than that observed with normal rabbit IgG. Four to 15 μg of insulin receptor antibody stimulated [32P]GDP release by 12-22% (P 〈 .05) and 7-14% in rat and human membranes, respectively. These results indicate that ligand binding to the insulin receptor results in a functional interaction of the receptor with a guanine nucleotide-binding transducer protein (G protein) and activation of GTP/GDP exchange.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Oecologia 18 (1975), S. 243-249 
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Investigations were carried out to study the allelopathic potentialities of Aristida adscensionis Linn. Bacterial culture experiments conducted have revealed that extracts of root, shoot and litter bring about a significant inhibition on the development of bacterial colonies of Azotobacter. When soil samples have been treated with these extracts, the soil nitrogen level has been diminished significantly in the soil samples treated with root extract, whereas with shoot extract the reduction in the soil nitrogen level was not significant. With litter leachate the depletion is found to be statistically significant at the 5% level. Thus it is concluded that Aristida adscensionis inhibits nitrogen fixing bacteria and thus creates a depleted nitrogen content in the soil. It is fairly probable that this may be a mechanism by which the species avoids competition from other species requiring good amounts of soil nitrogen for their metabolism. These results provide a possible explanation for the dominance of this grass species in the abandoned fields at Rajkot.
    Type of Medium: Electronic Resource
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