Guillemette G, Balla T, Baukal A J, Spät A, Catt K J
J Biol Chem. 1987 Jan 25;262(3):1010-5.
Many cells (including angiotensin II target cells) respond to external stimuli with accelerated hydrolysis of phosphatidylinositol 4,5-bisphosphate, generating 1,2-diacylglycerol and inositol 1,4,5-trisphosphate, a rapidly diffusible and potent Ca2+-mobilizing factor. Following its production at the plasma membrane level, inositol 1,4,5-trisphosphate is believed to interact with specific sites in the endoplasmic reticulum and triggers the release of stored Ca2+. Specific receptor sites for inositol 1,4,5-trisphosphate were recently identified in the bovine adrenal cortex (Baukal, A. J., Guillemette, G., Rubin, R., Spät, A., and Catt, K. J. (1985) Biochem. Biophys. Res. Commun. 133, 532-538) and have been further characterized in the adrenal cortex and other target tissues. The inositol 1,4,5-trisphosphate-binding sites are saturable and present in low concentration (104 +/- 48 fmol/mg protein) and exhibit high affinity for inositol 1,4,5-trisphosphate (Kd 1.7 +/- 0.6 nM). Their ligand specificity is illustrated by their low affinity for inositol 1,4-bisphosphate (Kd approximately 10(-7) M), inositol 1-phosphate and phytic acid (Kd approximately 10(-4) M), fructose 1,6-bisphosphate and 2,3-bisphosphoglycerate (Kd approximately 10(-3) M), with no detectable affinity for inositol 1-phosphate and myo-inositol. These binding sites are distinct from the degradative enzyme, inositol trisphosphate phosphatase, which has a much lower affinity for inositol trisphosphate (Km = 17 microM). Furthermore, submicromolar concentrations of inositol 1,4,5-trisphosphate evoked a rapid release of Ca2+ from nonmitochondrial ATP-dependent storage sites in the adrenal cortex. Specific and saturable binding sites for inositol 1,4,5-trisphosphate were also observed in the anterior pituitary (Kd = 0.87 +/- 0.31 nM, Bmax = 14.8 +/- 9.0 fmol/mg protein) and in the liver (Kd = 1.66 +/- 0.7 nM, Bmax = 147 +/- 24 fmol/mg protein). These data suggest that the binding sites described in this study are specific receptors through which inositol 1,4,5-trisphosphate mobilizes Ca2+ in target tissues for angiotensin II and other calcium-dependent hormones.
许多细胞（包括血管紧张素II靶细胞）对外部刺激的反应是加速水解磷脂酰肌醇4,5 - 二磷酸，生成1,2 - 二酰甘油和肌醇1,4,5 - 三磷酸，后者是一种可快速扩散且能有效动员钙离子的因子。在质膜水平产生后，肌醇1,4,5 - 三磷酸被认为会与内质网中的特定位点相互作用，并触发储存钙离子的释放。最近在牛肾上腺皮质中鉴定出了肌醇1,4,5 - 三磷酸的特异性受体位点（鲍卡尔，A. J.，吉耶梅特，G.，鲁宾，R.，施帕特，A.，和卡特，K. J.（1985年）《生物化学与生物物理研究通讯》133，532 - 538），并且在肾上腺皮质和其他靶组织中对其进行了进一步的特性描述。肌醇1,4,5 - 三磷酸结合位点具有饱和性，以低浓度存在（104±48飞摩尔/毫克蛋白质），并且对肌醇1,4,5 - 三磷酸表现出高亲和力（解离常数1.7±0.6纳摩尔）。它们对肌醇1,4 - 二磷酸（解离常数约10⁻⁷摩尔）、肌醇1 - 磷酸和植酸（解离常数约10⁻⁴摩尔）、果糖1,6 - 二磷酸和2,3 - 二磷酸甘油酸（解离常数约10⁻³摩尔）的低亲和力，以及对肌醇1 - 磷酸和肌醇无可检测的亲和力，说明了它们的配体特异性。这些结合位点与降解酶肌醇三磷酸磷酸酶不同，后者对肌醇三磷酸的亲和力要低得多（米氏常数 = 17微摩尔）。此外，亚微摩尔浓度的肌醇1,4,5 - 三磷酸会引起肾上腺皮质中非线粒体ATP依赖储存位点的钙离子快速释放。在垂体前叶（解离常数 = 0.87±0.31纳摩尔，最大结合容量 = 14.8±9.0飞摩尔/毫克蛋白质）和肝脏（解离常数 = 1.66±0.7纳摩尔，最大结合容量 = 147±24飞摩尔/毫克蛋白质）中也观察到了肌醇1,4,5 - 三磷酸的特异性和饱和性结合位点。这些数据表明，本研究中描述的结合位点是特异性受体，通过这些受体，肌醇1,4,5 - 三磷酸在血管紧张素II和其他钙依赖性激素的靶组织中动员钙离子。
