ラット肝細胞によるビタミンB_<12>結合タンパクの摂取とそれらの受容体の局在

概要

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Plasma contains two B_<12> binding proteins, R-binder (R) and transcobalamin (Tc) II. Their physiological functions are not well defined. In this study based on the known lack of species specificity with these binders, R was purified from desiccated hog stomach mucosa and Tc-II from human plasma Cohn fraction III using affinity chromatography. These proteins were complexed with [^<57>Co] B_<12> and given to rats i.v. and organ distribution was measured 5min. later. More than 90% of radioactivity was recovered from the liver when R-B_<12> was given, but it was significantly reduced if rats were pretreated with intravenous asialofetuin; the reduction was minimal with fetuin treatment. Tc-II-B_<12> was distributed more evenly among organs and uptake by the liver was not inhibited by asialofetuin. Hepatic parenchymal cells were separated by collagenase perfusion and density gradient using metrizamide, and in vitro uptake of R-and Tc-II-B_<12> by these cells was studied. Uptake of R-B_<12> was also inhibited by coexistent asialofetuin and asialomucin, but the uptake of Tc-II-B_<12> was not. These results suggest that R belongs to the group of asialoglycoproteins which is taken up by its specific receptor, asialoglycoprotein receptor, whereas Tc-II has a different system for uptake which perhaps involves another specific receptor.
日本ビタミン学会の論文
1989-06-25