title: Effect of guanine nucleotides on [3H]glutamate binding and on adenylate cyclase activity in rat brain membranes.
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.
authors.affiliation: Departamento de Quimica, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria, RS, Brasil.
authors.forename: M A
authors.initials: MA
authors.lastname: Rubin
authors.forename: A C
authors.initials: AC
authors.lastname: Medeiros
authors.forename: P C
authors.initials: PC
authors.lastname: Rocha
authors.forename: C B
authors.initials: CB
authors.lastname: Livi
authors.forename: G
authors.initials: G
authors.lastname: Ramirez
authors.forename: D O
authors.initials: DO
authors.lastname: Souza
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism*; D006150:Guanine Nucleotides / Q000378:metabolism / Q000494:pharmacology*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D006157:Guanosine Monophosphate / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism; D006165:Guanylyl Imidodiphosphate / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000494:pharmacology; D013873:Thionucleotides / Q000494:pharmacology; D014316:Tritium
chemical_list: D006150:Guanine Nucleotides; D013873:Thionucleotides; D014316:Tritium; D006153:Guanosine Diphosphate; D006165:Guanylyl Imidodiphosphate; D018698:Glutamic Acid; C023427:guanosine 5'-O-(2-thiodiphosphate); D006157:Guanosine Monophosphate; D006160:Guanosine Triphosphate; D012964:Sodium; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D008274:Magnesium