Role of Inositol Polyphosphates in Ca^<2+> Homeostasis

合成了一系列肌醇1.4.5-三磷酸酯（IP_3）类似物，在肌醇环的第2个碳上有一个庞大的取代基，并对其进行了研究，以探讨IP_3-5-磷酸酶的构效关系。IP_3-3激酶和IP_3结合蛋白。所有类似物（消旋混合物）都抑制红细胞鬼影催化的[^3H] IP_3的水解。与IP_3相比，Ki值更低。在此过程中发现有效的对映体为l型。这些类似物能够抑制脑细胞质将[^3H] IP_3磷酸化为[^3H] IP_4。虽然需要比IP_3更高的浓度。通过降低游离Ca^<2+>，抑制所需的浓度降低。在这个反应中。d -对映体有效。这些化合物的d -对映体也抑制了[^3H] IP_3与小脑微粒体的结合，其效力与IP_3相同。它们作为完全激动剂从渗透巨噬细胞释放Ca^<2+>。这些结果表明，IP_3的第2位可以在几种检测系统中进行修饰，而效价仅略有降低。因此，本文合成的IP_3类似物可以与其他分子连接而不损失其生物活性。例如，将IP_3类似物与Sepharose 4B偶联制成IP_3亲和柱，证明该亲和柱可用于纯化IP_3识别蛋白。

A series of inositol 1.4.5-trisphosphate (IP_3) analogs, with a bulky substituent on the 2nd carbon of the inositol ring, has been synthesized and examined to explore the structure-activity relationships among IP_3-5-phosphatase. IP_3-3-kinase, and IP_3 binding protein. All analogs (racemic mixtures) inhibited the hydrolysis of [^3H] IP_3 catalyzed by erythrocyte ghosts. With a lower Ki value than seen with IP_3. The effective enantiomer in this process was found to be L-type. The analogs were capable of inhibiting the phosphorylation of [^3H] IP_3 to [^3H] IP_4 by brain cytosol. Although higher concentrations than IP_3 were required. By lowering free Ca^<2+>, the concentrations required for the inhibition became low. In this reaction. the D-enantiomer was effective. The D-enantiomer of these compoundsalso inhibited the binding of [^3H] IP_3 to cerebellum microsomes, With the same potency as seen with IP_3. And they acted as a full agonists in releasing Ca^<2+> from permeabilized macrophages. These results indicate that the 2nd position of IP_3 can be modified with only minor reduction in potency in several assay systems. Thus, the IP_3 analogs synthesized here may be linked to other molecules without loss of their biological activities. For example, the IP_3 analogs were coupled with Sepharose 4B to make IP_3 affinity columns, and the columns were proved to be useful for purifying the IP_3-recognizing proteins.