Hu W L, Chindemi P A, Regoeczi E
Department of Pathology, McMaster University Health Sciences Centre, Hamilton, Ontario, Canada.
Biol Met. 1991;4(2):90-4. doi: 10.1007/BF01135384.
Rat aglycotransferrin (rAgTf) was produced from the disialosyl diantennary fraction of rat transferrin (rTf) by treatment with peptide: N-glycosidase F. Following removal of the enzyme by gel filtration and isolation of the deglycosylated protein by lectin chromatography, rAgTf was compared to rTf both in vitro and in vivo. No significant differences were found between the two proteins with respect to affinity for iron and kinetics of Fe release from the N-lobe and C-lobe. The fluorescence emission spectrum of apo-rTf was red-shifted by approximately 3 nm relative to diferric rTf; however, no spectral difference was detected between rTf and rAgTf when the analogous forms (apo or diferric) were compared. Plasma clearance of radioactive iron administered to rats as either rTf or rAgTf was comparable. Reticulocytes took up iron from rAgTf slightly faster than from rTf. In contrast, Fe acquisition by the liver from rAgTf was significantly reduced relative to rTf. This finding contrasts sharply with earlier observations with asialotransferrin (rAsTf) and provides a basis for discounting charge loss as the mechanism of enhanced hepatic Fe uptake from rAsTf. It is suggested that the glycan complement of rTf, while unimportant for interaction of the protein with specific receptors, probably plays a role in the interaction with low-affinity hepatic binding sites.
N-糖苷酶F处理大鼠转铁蛋白（rTf）的二唾液酸二天线部分来制备大鼠去糖基转铁蛋白（rAgTf）。通过凝胶过滤去除酶并用凝集素色谱法分离去糖基化蛋白后，在体外和体内将rAgTf与rTf进行比较。在铁亲和力以及铁从N叶和C叶释放的动力学方面，两种蛋白质之间未发现显著差异。脱铁rTf的荧光发射光谱相对于三价铁rTf红移了约3nm；然而，当比较类似形式（脱铁或三价铁）时，在rTf和rAgTf之间未检测到光谱差异。给予大鼠的放射性铁作为rTf或rAgTf时，其血浆清除率相当。网织红细胞从rAgTf摄取铁的速度比从rTf略快。相反，相对于rTf，肝脏从rAgTf摄取铁的量显著减少。这一发现与早期关于去唾液酸转铁蛋白（rAsTf）的观察结果形成鲜明对比，并为否定电荷损失作为肝脏从rAsTf摄取铁增加的机制提供了依据。有人提出，rTf的聚糖部分虽然对蛋白质与特定受体的相互作用不重要，但可能在与低亲和力肝脏结合位点的相互作用中起作用。
