Hilfiker H, Hattenhauer O, Traebert M, Forster I, Murer H, Biber J
Institut of Physiology, University Zürich, CH-8057 Zurich, Switzerland.
Proc Natl Acad Sci U S A. 1998 Nov 24;95(24):14564-9. doi: 10.1073/pnas.95.24.14564.
An isoform of the mammalian renal type II Na/Pi-cotransporter is described. Homology of this isoform to described mammalian and nonmammalian type II cotransporters is between 57 and 75%. Based on major diversities at the C terminus, the new isoform is designed as type IIb Na/Pi-cotransporter. Na/Pi-cotransport mediated by the type IIb cotransporter was studied in oocytes of Xenopus laevis. The results indicate that type IIb Na/Pi-cotransport is electrogenic and in contrast to the renal type II isoform of opposite pH dependence. Expression of type IIb mRNA was detected in various tissues, including small intestine. The type IIb protein was detected as a 108-kDa protein by Western blots using isolated small intestinal brush border membranes and by immunohistochemistry was localized at the luminal membrane of mouse enterocytes. Expression of the type IIb protein in the brush borders of enterocytes and transport characteristics suggest that the described type IIb Na/Pi-cotransporter represents a candidate for small intestinal apical Na/Pi-cotransport.
本文描述了一种哺乳动物肾II型钠/磷酸共转运体的亚型。该亚型与已描述的哺乳动物和非哺乳动物II型共转运体的同源性在57%至75%之间。基于C末端的主要差异，新亚型被设计为IIb型钠/磷酸共转运体。在非洲爪蟾卵母细胞中研究了由IIb型共转运体介导的钠/磷酸共转运。结果表明，IIb型钠/磷酸共转运是生电性的，且与肾II型亚型的pH依赖性相反。在包括小肠在内的各种组织中检测到了IIb型mRNA的表达。使用分离的小肠刷状缘膜通过蛋白质免疫印迹法检测到IIb型蛋白为108 kDa的蛋白质，并且通过免疫组织化学法将其定位在小鼠肠上皮细胞的腔膜上。IIb型蛋白在肠上皮细胞刷状缘中的表达及其转运特性表明，所描述的IIb型钠/磷酸共转运体是小肠顶端钠/磷酸共转运的一个候选者。
