Markovich D, Forgo J, Stange G, Biber J, Murer H
Institute of Physiology, University of Zürich, Switzerland.
Proc Natl Acad Sci U S A. 1993 Sep 1;90(17):8073-7. doi: 10.1073/pnas.90.17.8073.
Injection of rat kidney cortex mRNA into Xenopus laevis oocytes leads to a stimulation of Na(+)-dependent SO4(2-) uptake. Based on this information, we have isolated from a corresponding library a cDNA (NaSi-1) that is most likely related to a Na+/SO4(2-) cotransport system. NaSi-1 cRNA leads in a time- and dose-dependent manner to specific stimulation of Na(+)-dependent SO4(2-) uptake in oocytes. The apparent affinity constants of the NaSi-1 cRNA-expressed transport resemble those of Na+/SO4(2-) cotransport in brush-border membrane. The NaSi-1 cDNA contains 2239 bp [including a poly(A) tail] and encodes a protein of 595 amino acids (66.05 kDa); the hydropathy profile suggests at least eight membrane-spanning regions. In vitro translation of NaSi-1 cRNA results in a protein of the expected size and suggests glycosylation. Northern blot analysis shows signals of 2.3 and 2.9 kb in kidney (more abundant in cortex than in papilla/medulla) and in mucosa of small intestine of rats. The above data indicate that we have structurally identified a membrane protein involved in renal and small-intestinal brush-border membrane Na+/SO4(2-) cotransport.
将大鼠肾皮质mRNA注射到非洲爪蟾卵母细胞中会刺激Na⁺依赖性SO₄²⁻摄取。基于此信息，我们从相应文库中分离出一个cDNA（NaSi-1），它很可能与Na⁺/SO₄²⁻共转运系统相关。NaSi-1 cRNA以时间和剂量依赖性方式特异性刺激卵母细胞中Na⁺依赖性SO₄²⁻摄取。NaSi-1 cRNA表达的转运的表观亲和常数类似于刷状缘膜中Na⁺/SO₄²⁻共转运的表观亲和常数。NaSi-1 cDNA包含2239 bp（包括一个聚腺苷酸尾），编码一个595个氨基酸（66.05 kDa）的蛋白质；亲水性图谱显示至少有八个跨膜区域。NaSi-1 cRNA的体外翻译产生预期大小的蛋白质，并提示存在糖基化。Northern印迹分析显示在大鼠肾脏（皮质比乳头/髓质更丰富）和小肠黏膜中有2.3和2.9 kb的信号。上述数据表明，我们在结构上鉴定了一种参与肾和小肠刷状缘膜Na⁺/SO₄²⁻共转运的膜蛋白。
