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Studies on Physiological Roles of Protein Phosphatases in Mammalian Smooth Muscle Tissues

哺乳动物平滑肌组织中蛋白磷酸酶的生理作用研究

基本信息

批准号：
01570062
负责人：
TAKAI Akira
金额：
$ 1.34万
依托单位：
Nagoya University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1989
资助国家：
日本
起止时间：
1989 至 1990
项目状态：
已结题

项目摘要

In mammalian smooth muscle tissues, the composition and physiological functions of protein phosphatases have been studied with the use of okadaic acid (OA), a potent inhibitor of type 2A and type 1 protein phosphatases, and inhibitor 2, an intrinsic inhibitory factor of type 1 phosphatase. We have obtained the following results :[1] In the extracts of smooth muscle tissues of guinea-pig, we have identified the following four distinct protein phosphatase activities : an inhibitor 2-sensitive (type 1) phosphatase activity which is susceptible to OA, a Mg^<2+>-dependent and OA-insensitive (type 2C) phosphatase activity, and two type 2A-like phosphatase activities with different susceptibilities to OA. We have also obtained results indicating that the type 2A-like fraction with lower affinity to okadaic acid may be responsible for dephosphorylation of myosin light chains to induce relaxation of smooth muscle.[2] In isolated myocytes of rabbit trachea, we have shown that the openstate probability of Ca^<2+>-dependent K^+-channel is reversibly increased by either extracellular application of isoprenaline or intracellular application of protein kinase A. We have also observed that this effect is significantly enhanced and prolonged in the presence of okadaic acid.[3] So far the dephosphorylation of p-nitrophenyl phosphate (pNPP) by protein phosphatase preparations has been thought to be due to contamination by alkaline phosphatases. We have found that the activity of protein phosphatases are very susceptible to OA, to the same extent as is their activity against phosphorylated proteins. As OA has been shown to have no effect on alkaline phosphatases, this result indicates that the activity against pNPP is intrinsic to the protein phosphatases.

在哺乳动物的平滑肌组织中，用冈田酸和抑制因子2研究了蛋白磷酸酶的组成和生理功能。冈田酸是2A型和1型蛋白磷酸酶的有效抑制剂，而抑制剂2是1型磷酸酶的内在抑制因子。结果如下：[1]在豚鼠平滑肌组织的提取液中，我们鉴定了四种不同的蛋白磷酸酶活性：一种是对OA敏感的抑制物2敏感的(类型1)磷酸酶活性，一种是依赖于镁离子的和对OA不敏感的(类型2C)磷酸酶活性，另一种是对OA易感性不同的两种类型的类2A型磷酸酶活性。我们还获得了结果，表明对冈田酸亲和力较低的2A型类组分可能与肌球蛋白轻链去磷酸化导致平滑肌松弛有关。[2]在兔气管分离的心肌细胞上，我们证明了Ca^&lt；2+&gt；细胞外应用异丙肾上腺素或细胞内应用蛋白激酶A可逆地增加依赖的K~(++)通道。我们还观察到，这种作用在冈田酸的存在下显著增强和延长。[3]到目前为止，蛋白磷酸酶制剂对对-硝基苯基磷酸(PNPP)的去磷酸化被认为是由于碱性磷酸酶的污染。我们已经发现，蛋白磷酸酶的活性非常容易受到OA的影响，就像它们对磷酸化蛋白的活性一样。由于OA已被证明对碱性磷酸酶没有影响，这一结果表明对pNPP的活性是蛋白质磷酸酶所固有的。