Bartfai T, Breakefield X O, Greengard P
Biochem J. 1978 Oct 15;176(1):119-27. doi: 10.1042/bj1760119.
The increase in intracellular cyclic GMP concentrations in response to muscarinic-receptor activation in N1E-115 neuroblastoma cells is dependent on extracellular Ca2+ ion. The calcium ionophore A23187 can also evoke an increase in cyclic GMP in the presence of Ca2+ ion. Most (about 85%) of the guanylate cyclase activity of broken-cell preparations is found in the soluble fraction. The soluble enzyme can utilize MnGTP (Km = 55 micrometer), MgGTP (Km = 310 micrometer) and CaGTP (Km greater than 500 micrometer) as substrates. Free GTP is a strong competitive inhibitor (Ki approximately 20 micrometer). The enzyme possesses an allosteric binding site for free metal ions (Ca2+, Mg2+ and Mn2+). The membrane-bound guanylate cyclase is qualitatively similar to the soluble form, but has lower affinity for the metal-GTP substrates. Entry of Ca2+ into cells may increase cyclic GMP concentration by activating guanylate cyclase through an indirect mechanism.
N1E - 115神经母细胞瘤细胞中,毒蕈碱受体激活后细胞内环鸟苷酸(cGMP)浓度的增加依赖于细胞外钙离子(Ca2+)。在有钙离子存在的情况下,钙离子载体A23187也能引起cGMP增加。破碎细胞制剂中大部分(约85%)的鸟苷酸环化酶活性存在于可溶部分。可溶性酶能够利用锰鸟苷三磷酸(MnGTP,Km = 55微米)、镁鸟苷三磷酸(MgGTP,Km = 310微米)和钙鸟苷三磷酸(CaGTP,Km大于500微米)作为底物。游离鸟苷三磷酸(GTP)是一种强竞争性抑制剂(Ki约为20微米)。该酶具有一个针对游离金属离子(Ca2+、Mg2+和Mn2+)的别构结合位点。膜结合鸟苷酸环化酶在性质上与可溶形式相似,但对金属 - GTP底物的亲和力较低。钙离子进入细胞可能通过间接机制激活鸟苷酸环化酶,从而增加cGMP浓度。