Ultrastructural localization of γ‐glutamyl transpeptidase in rat kidney and jejunum
Ultrastructural localization of γ‐glutamyl transpeptidase in rat kidney and jejunum
复制标题
大鼠肾和空肠中γ-谷氨酰转肽酶的超微结构定位
DOI：
10.1016/0014-5793(79)80425-1
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发表时间：
1979
期刊：
影响因子：
3.5
通讯作者：
S. Tate
中科院分区：
文献类型：
--
作者：
G. Marathe;B. Nash;R. Haschemeyer;S. Tate
1.γ-谷氨酰转肽酶是一种膜结合酶，通过将γ-谷氨酰部分转移到许多受体如氨基酸、肽和水来催化谷胱甘肽降解代谢的初始步骤。在肾近端小管、空肠绒毛、脉络丛、胆管、精囊、附睾和睫状体的上皮细胞中发现该酶的高活性，与其在转运过程中的作用一致[1，2]。光镜水平的组织化学研究表明，该酶定位于肾和空肠上皮细胞的刷状缘[2]。亚细胞分级分离研究支持了这一推断，该研究表明酶活性在刷状缘膜中富集[3-lo]。然而，这些结论受到了质疑，声称该酶既不位于肾刷状缘膜，也不位于基底外侧膜[11，121]。我们在这里报告的超微结构定位的γ-谷氨酰转肽酶在组织切片，提供了直接的证据，该酶确实主要位于刷状缘膜的大鼠肾脏近端小管和空肠绒毛的尖端细胞。在肾小球足细胞足突的膜中也观察到活性。此外，免疫细胞化学研究，使用铁蛋白抗体缀合物和木瓜蛋白酶处理的完整膜囊泡的结果表明，酶位于刷状缘膜的外（腔）表面上。这种定位与酶代谢细胞外谷胱甘肽以及细胞内谷胱甘肽易位到膜的能力一致
1. Introduction y-Glutamyl transpeptidase, a membrane-bound enzyme, catalyzes the initial step in the degradative metabolism of glutathione by transferring the y-glutamyl moiety to a number of acceptors such as amino acids, peptides and water. High activities of this enzyme are found in epithelial cells of the renal proximal tubules, jejunal villi, choroid plexus, bile ducts, seminal vesicles, epididymis, and ciliary body, consistent with its proposed role in transport processes [1, 2]. Histochemical studies at light microscopic level were suggestive of the enzyme’s localization in the brush border of renal and jejunal epithelial cells [2]. This inference has been supported by subcellular fractionation studies which showed that the enzyme activity was enriched in brush border membranes [3-lo]. However, these conclusions have been challenged by claims that the enzyme is neither localized in the renal brush border membranes nor in the basallateral membranes [11, 121. We report here the ultrastructural localization of y-glutamyl transpeptidase in tissue slices that provides direct evidence that the enzyme is indeed primarily located in the brush border membranes of the rat kidney proximal tubules and of the tip cells of the jejunal villi. Activity is also seen in the membranes of the foot processes of glo-merular podocytes. Furthermore, immunocytochemical studies using ferritin-antibody conjugates and results from papain treatment of intact membrane vesicles show that the enzyme is located on the outer (luminal) surface of the brush border membranes. Such localization is consistent with the enzyme’s ability to metabolize both extracellular glutathione as well as intracellular glutathione translocated to membrane