Rubin M A, Medeiros A C, Rocha P C, Livi C B, Ramirez G, Souza D O
Departamento de Quimica, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria, RS, Brasil.
Neurochem Res. 1997 Feb;22(2):181-7. doi: 10.1023/a:1027367624250.
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.
GMP-PNP是一种不可水解的GTP类似物，在Mg2+存在的情况下能紧密结合G蛋白，以至于即使经过彻底洗涤，这种结合依然稳定。利用这一特性制备了大鼠脑的膜样本，其中G蛋白的GTP结合位点被GMP-PNP饱和。用这些膜进行的实验表明，GTP、GMP-PNP、GDP-S和GMP（1 mM）可使不依赖钠的[3H]谷氨酸结合抑制30 - 40%[F(4,40) = 5.9；p <.001]，而只有GMP-PNP能激活腺苷酸环化酶活性[F(6,42) = 3.56；p <.01]。不依赖钠的[3H]谷氨酸结合的抑制在没有Mg2+的情况下也会发生。这些发现表明，鸟嘌呤核苷酸可能通过作用于不同位点，通过不同机制抑制谷氨酸结合并激活腺苷酸环化酶。
