Effect of Guanine Nucleotides on [3H]Glutamate Binding and on Adenylate Cyclase Activity in Rat Brain Membranes |
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Authors: | Rubin Maribel A. Medeiros Alan C. Rocha Paula C. B. Livi Carolina B. Ramirez Galo Souza Diogo O. |
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Affiliation: | (1) Departamento de Quimica, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria, 97119-900 Santa Maria, RS, Brasil;(2) Departamento de Bioquimica, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil;(3) Centro de Biologia Molecular (CSIC-UAM), Universidade Autónoma, Canto Blanco, 28049 Madrid, Spain |
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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. |
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Keywords: | Glutamate [3H]glutamate-binding guanine nucleotides adenylate cyclase G-proteins |
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