RESUMO

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.

Assuntos

Adenilil Ciclases/metabolismo , Encéfalo/metabolismo , Ácido Glutâmico/metabolismo , Nucleotídeos de Guanina/farmacologia , Animais , Encéfalo/efeitos dos fármacos , Membrana Celular/metabolismo , Proteínas de Ligação ao GTP/metabolismo , Nucleotídeos de Guanina/metabolismo , Guanosina Difosfato/análogos & derivados , Guanosina Difosfato/farmacologia , Guanosina Monofosfato/farmacologia , Guanosina Trifosfato/metabolismo , Guanilil Imidodifosfato/metabolismo , Magnésio/farmacologia , Masculino , Ratos , Ratos Wistar , Sódio/farmacologia , Tionucleotídeos/farmacologia , Trítio