镁离子在激素刺激大鼠骨肉瘤腺苷酸环化酶中的作用。

The role of Mg2+ in hormone stimulation of rat osteosarcoma adenylate cyclase.

Rodan S B, Rodan G A

Biochim Biophys Acta. 1981 Feb 18;673(1):55-63.

Abstract

Mg2+ concentration dependence of adenylate cyclase activity, in a rat osteosarcoma cell line (ROS 2/3), exhibits two apparent affinities with Km values of approx. 2 mM and 10 mM. 2. Only one Mg2+ affinity with a Km value of around 1 mM was apparent at saturating concentrations of: (i) guanosine-5'-(beta, gamma-imido)triphosphate; (ii) parathyroid hormone and GTP; and (iii) (-)-isoproterenol and GTP. 3. Conversely, at saturating concentrations of Mg2+ (40 mM) only high hormone concentrations, acting on low affinity sites, stimulated adenylate cyclase. 4. At saturating concentrations of guanosine-5'-(beta, gamma-imido)triphosphate, hormone stimulation decreased with increasing Mg2+ concentrations and none was seen at 40 mM Mg2+. The findings suggest that hormone stimulation of adenylate cyclase is associated with Mg2+ activation of a 'high hormone affinity' responsive state dependent on triphosphoguanine nucleotide. The hormone effect on Mg2+ affinity fully accounts for hormone stimulation of adenylate cyclase at physiologically relevant concentrations.

摘要

在大鼠骨肉瘤细胞系（ROS 2/3）中，腺苷酸环化酶活性对Mg2+浓度的依赖性呈现出两种明显的亲和力，其Km值约为2 mM和10 mM。2. 在以下饱和浓度下，仅出现一种Km值约为1 mM的Mg2+亲和力：（i）鸟苷-5'-（β，γ-亚氨基）三磷酸；（ii）甲状旁腺激素和GTP；以及（iii）（-）-异丙肾上腺素和GTP。3. 相反，在Mg2+饱和浓度（40 mM）下，只有高浓度激素作用于低亲和力位点时，才会刺激腺苷酸环化酶。4. 在鸟苷-5'-（β，γ-亚氨基）三磷酸饱和浓度下，激素刺激随Mg2+浓度增加而降低，在40 mM Mg2+时未观察到刺激作用。这些发现表明，激素对腺苷酸环化酶的刺激与依赖于三磷酸鸟嘌呤核苷酸的“高激素亲和力”反应状态的Mg2+激活有关。在生理相关浓度下，激素对Mg2+亲和力的影响完全解释了激素对腺苷酸环化酶的刺激作用。