Moran A, Davis L J, Turner R J
Department of Physiology, Armed Forces Radiobiological Research Institute, Bethesda, Maryland 20892.
J Biol Chem. 1988 Jan 5;263(1):187-92.
The phlorizin binding properties of luminal membrane vesicles isolated from the LLC-PK1 cells, a continuous epithelial cell line derived from pig kidney, are studied. Scatchard analysis of this binding indicates the existence of a single high affinity sodium-dependent site with KD = 0.4 microM at 266 mM sodium. The specificity properties of this site indicate that it represents the binding of phlorizin to the hexose binding site of the sodium-dependent D-glucose transporter previously identified in this cell line. Both phlorizin equilibrium binding and the rate of phlorizin binding were found to be sigmoidal functions of sodium concentration. A Hill analysis of these data was consistent with a sodium:phlorizin stoichiometry of 2:1 in good agreement with the sodium:glucose stoichiometry already established in these cells. Phlorizin dissociation was also found to be sodium-dependent. On the basis of the phlorizin binding data presented here, a number of models of the binding of phlorizin and sodium to the transporter can be excluded. An analysis of a random binding model consistent with the data is presented. The significance of the LLC-PK1 sodium-dependent D-glucose transporter as a model system for related renal and intestinal transporters is discussed.
对从LLC-PK1细胞（一种源自猪肾的连续上皮细胞系）中分离出的管腔膜囊泡的根皮苷结合特性进行了研究。对这种结合的Scatchard分析表明，在266 mM钠浓度下存在一个单一的高亲和力钠依赖性位点，KD = 0.4 μM。该位点的特异性特性表明，它代表根皮苷与先前在该细胞系中鉴定出的钠依赖性D-葡萄糖转运蛋白的己糖结合位点的结合。发现根皮苷平衡结合和根皮苷结合速率均为钠浓度的S形函数。对这些数据的Hill分析与钠：根皮苷化学计量比为2:1一致，这与这些细胞中已确定的钠：葡萄糖化学计量比非常吻合。还发现根皮苷解离是钠依赖性的。基于此处给出的根皮苷结合数据，可以排除一些根皮苷和钠与转运蛋白结合的模型。提出了一个与数据一致的随机结合模型分析。讨论了LLC-PK1钠依赖性D-葡萄糖转运蛋白作为相关肾和肠转运蛋白模型系统的意义。
