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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 22 (1997), S. 181-187 
    ISSN: 1573-6903
    Keywords: Glutamate ; [3H]glutamate-binding ; guanine nucleotides ; adenylate cyclase ; G-proteins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract GMP-PNP, a non-hydrolyzable analog of GTP binds tightly to G-protein in the presence of Mg2+, so that the binding is stable even after exhaustive washings. This property was exploited to prepare membrane samples of rat brain where G-protein GTP-binding sites were saturated with GMP-PNP. Experiments carried out with these membranes showed that GTP, GMP-PNP, GDP-S and GMP (1 mM) inhibit the sodium-independent [3H]glutamate binding by 30–40% [F(4,40) = 5.9; p 〈 .001], whereas only GMP-PNP activates adenylate cyclase activity [F(6,42) = 3.56; p 〈 .01]. The inhibition of sodium-independent [3H]glutamate binding occurred in the absence of Mg2+. These findings suggest that guanine nucleotides may inhibit glutamate binding and activate adenylate cyclase through distinct mechanisms by acting on different sites.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 24 (1999), S. 1037-1042 
    ISSN: 1573-6903
    Keywords: Lead acetate ; adenylate cyclase ; 5′-guanylylimidodiphosphate ; forskolin ; cerebral cortex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Lead decreased in a dose dependent manner the basal AC activity in membranes of rat cerebral cortex (IC50 = 2.5 ± 0.1 μM). In membranes preincubated under basal conditions, AC activity was stimulated by approximately two and fourfold by 10 μM Gpp(NH)p or forskolin, respectively. Under basal conditions, lead (3 μM) inhibited enzyme activity up to 50%, but was not able to inhibit the Gpp(NH)p- or the forskolin-stimulated AC activity. However, in membranes preincubated with Gpp(NH)p (10 μM), lead (3 μM) had no significant effect on enzyme activity, but it partly blocked the stimulation of AC activity elicited by forskolin (10 μM). In membranes preincubated with 10 μM lead, the addition of 10 μM Gpp(NH)p or forskolin in the incubation medium did not stimulate AC activity. However, when added together in the incubation medium Gpp(NH)p + forskolin produced an increase in enzyme activity. In membranes preincubated with 10 μM lead + 10 μM Gpp(NH)p, Gpp(NH)p (10 μM) or forskolin (10 μM) added alone or in combination to the incubation medium did not stimulate AC activity. Moreover, under these latter conditions lead had no further effect on enzyme activity. These results indicate that lead may interact with G-proteins and with the catalytic subunit of cerebral cortical AC to produce inhibition of the enzyme activity.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Neurochemical research 20 (1995), S. 1437-1441 
    ISSN: 1573-6903
    Keywords: Pyroglutamic acid ; organic acidemias ; neurotoxicity ; adenylate cyclase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect ofl-pyroglutamic acid, a metabolite that accumulates in pyroglutamic aciduria, on different neurochemical parameters was investigated in adult male Wistar rats. Glutamate binding, adenylate cyclase activity and G protein coupling to adenylate cyclase were assayed in the presence of the acid.l-pyroglutamic acid decreased Na+-dependent and Na+-independent glutamate binding Basal and GMP-PNP stimulated adenylate cyclase activity were not affected by the acid. Furthermore, rats received unilateral intrastriatal injections of 10–300 nmol of bufferedl-pyroglutamic acid. Vehicle (0.25 M Tris-Cl, pH 7.35–7.4) was injected into the contralateral striatum. Neurotoxic damage was assessed seven days after the injection by histological examination and by weighing both cerebral hemispheres. No difference in histology or weight could be identified between hemispheres. These results suggest that, although capable of interfering with glutamate binding, pyroglutamate did not cause a major lesion in the present model of neurotoxicity.
    Type of Medium: Electronic Resource
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