Three types of human asialo-transferrin and their interactions with the rat liver.
Three types of human asialo-transferrin and their interactions with the rat liver.
复制标题
三种类型的人脱唾液酸转铁蛋白及其与大鼠肝脏的相互作用。
作者：
E. Regoeczi;P. Taylor;M. Debanne;L. März;M. Hatton
三种类型的无唾液酸转铁蛋白从免疫纯的人转铁蛋白通过层析在DEAE-纤维素，然后去唾液酸化和亲和层析柱上的固定化无唾液酸糖蛋白结合的肝凝集素从兔肝。在无唾液酸转铁蛋白中，1型衍生自转铁蛋白的主要DEAE-纤维素色谱组分，即含有两个双触角聚糖的组分。另外两种无唾液酸转铁蛋白（2型和3型）来源于次要的DEAE色谱转铁蛋白组分，假定其具有一个双触角和一个三触角聚糖。这三种无唾液酸转铁蛋白类型是无法区分的电泳迁移率，但他们很容易区分的基础上，其结合强度的肝凝集素在完整的大鼠。导致无唾液酸转铁蛋白2型和3型之间结合强度差异的聚糖结构尚不清楚。大鼠代谢研究表明，在低剂量（<1 μ g/100 g体重）下，没有一种单独的无唾液酸转铁蛋白类型能够产生内吞信号。因此，在注射后35分钟，大部分注射的蛋白质可被血浆和肝脏回收。然而，通过注射较大剂量（50- 250 μ g/100 g体重），很容易诱导每种无唾液酸转铁蛋白类型的内吞作用和catalysis。相同类型或不同类型的未标记的无唾液酸转铁蛋白在标记剂量后的短时间间隔内。这些发现支持肝细胞对人无唾液酸转铁蛋白的剂量依赖性摄取的观点，如在用由全转铁蛋白制备的无唾液酸转铁蛋白的早期研究中所建立的[Regoeczi，Taylor，Hatton，Wong & Koj（1978）Biochem.J.174，171-178]，也适用于这些无唾液酸转铁蛋白亚组分。此外，本研究表明，不同碳水化合物组成的无唾液酸转铁蛋白能够协同促进彼此的内吞作用。
Three types of asialo-transferrin were obtained from immunologically pure human transferrin by chromatography on DEAE-cellulose, followed by desialylation and affinity chromatography on a column of the immobilized asialo-glycoprotein-binding hepatic lectin from rabbit liver. Of the asialo-transferrins, type 1 was derived from the principal DEAE-cellulose chromatographic component of transferrin, i.e. the one that contains two biantennary glycans. The two other asialo-transferrins (types 2 and 3) were derived from a minor DEAE-chromatographic transferrin component, which is assumed to possess one biantennary and one triantennary glycan. The three asialo-transferrin types were indistinguishable by electrophoretic mobility, but they were readily distinguished on the basis of their binding strengths to the hepatic lectin in intact rats. Glycan structures responsible for the difference in binding strengths between asialo-transferrin types 2 and 3 are not known. Metabolic studies in rats showed that none of the individual asialo-transferrin types was capable of generating a signal for endocytosis at low doses (<1mug/100g body wt.) and, consequently, most of the injected protein was recoverable with the plasma and the liver 35min after injection. However, endocytosis and catabolism of each asialo-transferrin type was readily induced by injecting a larger dose (50-250mug/100g body wt.) of unlabelled asialo-transferrin of the same type or of a different type a short interval after the labelled dose. These findings support the view that the dose-dependent uptake of human asialo-transferrin by the hepatocyte, as established in an earlier study with asialo-transferrin made from whole transferrin [Regoeczi, Taylor, Hatton, Wong & Koj (1978) Biochem. J.174, 171-178], also holds for these asialo-transferrin subfractions. Furthermore, the present studies indicate that asialo-transferrins of different carbohydrate compositions are capable of synergistically promoting endocytosis of each other.