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Binding of vitamin B12--rat transcobalamin II and free vitamin B12 to plasma membranes isolated from rat liver.
Br J Haematol. 1975 Nov; 31(3):311-21.BJ

Abstract

When dialysed rat serum which contains a single, low molecular weight binder for vitamin B12, rat transcobalamin II (rat TC-II), was labelled in vitro with 57Co-vitamin B12 and then incubated at 30 degrees C (pH 7-5) with vesicles of highly purified plasma membranes separated from microsomal fractions of rat liver by density gradient centrifugation, the 57Co-vitamin B12-rat TC-II complex bound to high affinity sites on the vesicles via a specific (binding after correction for 'non-specific' binding in the presence of a large excess of the non-radioactive complex), saturable, and reversible interaction. The apparent affinity constant for the binding reaction was 5-5 X 10(9) M-1. Using the same incubation conditions, free vitamin B12 also bound to the vesicles of plasma membranes via a specific, saturable, but apparently irreversible interaction. Preincubation of the membranes with free vitamin B12 did not interfere with the subsequent binding of the vitamin B12-rat TC-II complex to the membranes; however, preincubation with the vitamin B12-rat TC-II complex did interfere, to some extent, with the subsequent binding of free vitamin B12. Dialysed rat serum, perhaps the free rat TC-II in the dialysed serum, also inhibited the binding of the vitamin B12-rat TC-II complex to the plasma membranes. The relationship of the binding sites identified in this report to the absorption of vitamin B12 by rat liver, and thus their physiological significance remains unknown until further work is done, perhaps using intact hepatocytes.

Authors

Fiedler-Nagy C
No affiliation info available
Rowley GR
No affiliation info available
Coffey JW
No affiliation info available
Miller ON
No affiliation info available

MeSH

AnimalsBinding SitesBiological TransportBlood ProteinsCalciumCell MembraneFemaleLiverRatsTranscobalaminsVitamin B 12

Pub Type(s)

Journal Article

Language

eng

PubMed ID

1201244

Citation

Fiedler-Nagy, C, et al. "Binding of Vitamin B12--rat Transcobalamin II and Free Vitamin B12 to Plasma Membranes Isolated From Rat Liver." British Journal of Haematology, vol. 31, no. 3, 1975, pp. 311-21.
Fiedler-Nagy C, Rowley GR, Coffey JW, et al. Binding of vitamin B12--rat transcobalamin II and free vitamin B12 to plasma membranes isolated from rat liver. Br J Haematol. 1975;31(3):311-21.
Fiedler-Nagy, C., Rowley, G. R., Coffey, J. W., & Miller, O. N. (1975). Binding of vitamin B12--rat transcobalamin II and free vitamin B12 to plasma membranes isolated from rat liver. British Journal of Haematology, 31(3), 311-21.
Fiedler-Nagy C, et al. Binding of Vitamin B12--rat Transcobalamin II and Free Vitamin B12 to Plasma Membranes Isolated From Rat Liver. Br J Haematol. 1975;31(3):311-21. PubMed PMID: 1201244.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Binding of vitamin B12--rat transcobalamin II and free vitamin B12 to plasma membranes isolated from rat liver. AU - Fiedler-Nagy,C, AU - Rowley,G R, AU - Coffey,J W, AU - Miller,O N, PY - 1975/11/1/pubmed PY - 1975/11/1/medline PY - 1975/11/1/entrez SP - 311 EP - 21 JF - British journal of haematology JO - Br J Haematol VL - 31 IS - 3 N2 - When dialysed rat serum which contains a single, low molecular weight binder for vitamin B12, rat transcobalamin II (rat TC-II), was labelled in vitro with 57Co-vitamin B12 and then incubated at 30 degrees C (pH 7-5) with vesicles of highly purified plasma membranes separated from microsomal fractions of rat liver by density gradient centrifugation, the 57Co-vitamin B12-rat TC-II complex bound to high affinity sites on the vesicles via a specific (binding after correction for 'non-specific' binding in the presence of a large excess of the non-radioactive complex), saturable, and reversible interaction. The apparent affinity constant for the binding reaction was 5-5 X 10(9) M-1. Using the same incubation conditions, free vitamin B12 also bound to the vesicles of plasma membranes via a specific, saturable, but apparently irreversible interaction. Preincubation of the membranes with free vitamin B12 did not interfere with the subsequent binding of the vitamin B12-rat TC-II complex to the membranes; however, preincubation with the vitamin B12-rat TC-II complex did interfere, to some extent, with the subsequent binding of free vitamin B12. Dialysed rat serum, perhaps the free rat TC-II in the dialysed serum, also inhibited the binding of the vitamin B12-rat TC-II complex to the plasma membranes. The relationship of the binding sites identified in this report to the absorption of vitamin B12 by rat liver, and thus their physiological significance remains unknown until further work is done, perhaps using intact hepatocytes. SN - 0007-1048 UR - https://www.unboundmedicine.com/medline/citation/1201244/Binding_of_vitamin_B12__rat_transcobalamin_II_and_free_vitamin_B12_to_plasma_membranes_isolated_from_rat_liver_ DB - PRIME DP - Unbound Medicine ER -