RECEPTOR-MEDIATED ENDOCYTOSIS OF THE INTRINSIC-FACTOR COBALAMIN COMPLEX IN HT-29, A HUMAN COLON-CARCINOMA CELL-LINE

A HT 29 cell line derived from human colonic carcinoma was shown to express the intrinsic factor receptor, with about 5000 binding sites per cell and an association constant of 20 x 10(9) 1/mol at pH 7.4 and 4-degrees-C. The number of binding sites increased dramatically between 7 and 10 days of culture time. Endocytosis of the intrinsic factor-cobalamin-receptor complex was inhibited by two ways: at 4-degrees-C and at 37-degrees-C by incubating the cells with vinblastine, monesin and chloroquine. The plasma membrane receptor was cross-linked to [Co-57]cobalamin-intrinsic factor and solubized with Triton X-100. The cross-linked complex had a relative molecular mass of 330 kDa in native PAGE.