Gazzano H, Wu H I, Waldman S A
Department of Medicine, Stanford University School of Medicine, Palo Alto, California.
Infect Immun. 1991 Apr;59(4):1552-7. doi: 10.1128/iai.59.4.1552-1557.1991.
Guanylate cyclase is regulated by adenine nucleotides in membranes of intestinal mucosal cells. Basal guanylate cyclase was activated about twofold by adenine nucleotides. Activation was specific for adenine, as compared with the pyrimidine nucleotides UTP and CTP. In addition, enzyme activation was obtained in the presence of saturating concentrations of GTP, the substrate for guanylate cyclase. The most potent adenine nucleotide was the nonhydrolyzable analog of ATP, adenosine 5'-O-(3-thiotriphosphate). Adenine nucleotide activation was specific for the particulate form of guanylate cyclase, as compared with the soluble form. Also, adenine nucleotides potentiated the activation of guanylate cyclase by the heat-stable enterotoxin produced by Escherichia coli. Indeed, enzyme activation by adenine nucleotides and toxin was greater than the sum of individual activations by these agents. Adenine nucleotides regulate guanylate cyclase by increasing the maximum velocity of the enzyme without altering its affinity for substrate or its cooperativity. In addition to stimulating guanylate cyclase, adenine nucleotides decreased the specific binding of the heat-stable enterotoxin to receptors in intestinal membranes. The coordinated regulation of the toxin-receptor interaction and guanylate cyclase activity by a process utilizing nonhydrolyzable analogs of a purine nucleotide is similar to the mechanisms involved in the hormone regulation of adenylate cyclase by guanine nucleotide-binding proteins. These data suggest that an adenine nucleotide-dependent protein may couple the toxin-receptor interaction to the regulation of particulate guanylate cyclase in intestinal membranes.
鸟苷酸环化酶受肠黏膜细胞膜中腺嘌呤核苷酸的调节。基础鸟苷酸环化酶被腺嘌呤核苷酸激活约两倍。与嘧啶核苷酸UTP和CTP相比，激活对腺嘌呤具有特异性。此外，在鸟苷酸环化酶底物GTP饱和浓度存在的情况下可实现酶的激活。最有效的腺嘌呤核苷酸是ATP的不可水解类似物，腺苷5'-O-(3-硫代三磷酸)。与可溶性形式相比，腺嘌呤核苷酸激活对颗粒形式的鸟苷酸环化酶具有特异性。此外，腺嘌呤核苷酸增强了大肠杆菌产生的热稳定肠毒素对鸟苷酸环化酶的激活作用。实际上，腺嘌呤核苷酸和毒素对酶的激活作用大于这些试剂单独激活作用的总和。腺嘌呤核苷酸通过增加酶的最大速度来调节鸟苷酸环化酶，而不改变其对底物的亲和力或协同性。除了刺激鸟苷酸环化酶外，腺嘌呤核苷酸还降低了热稳定肠毒素与肠膜受体的特异性结合。利用嘌呤核苷酸不可水解类似物的过程对毒素-受体相互作用和鸟苷酸环化酶活性进行的协同调节，类似于鸟嘌呤核苷酸结合蛋白对腺苷酸环化酶的激素调节机制。这些数据表明，一种依赖腺嘌呤核苷酸的蛋白质可能将毒素-受体相互作用与肠膜中颗粒状鸟苷酸环化酶的调节联系起来。
