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Characterization of ileal vitamin B12 Binding using homogeneous human and hog intrinsic factors.
J Clin Invest. 1973 Dec; 52(12):3074-83.JCI

Abstract

Elucidation of the mechanism of intrinsic factor (IF)-mediated vitamin B(12) (B(12)) binding to ileal binding sites has been hampered by the use of crude or only partially purified preparations of IF in previous studies. We have used homogeneous human IF and hog IF isolated by affinity chromatography to study [(57)Co]B(12) binding to ileal mucosal homogenates. The following observations were made: (a) Human IF-B(12) and hog IF-B(12) were bound to human, monkey, hog, dog, rabbit, mouse, hamster, and guinea pig ileal, but not jejunal, homogenates in amounts significantly greater than free B(12) or B(12) bound to five other homogeneous B(12)-binding proteins; (b) only IF-mediated B(12) binding was localized to ileal homogenates and was inhibited by EDTA; (c) values for the association constant (K(a)) for the various ileal homogenates mentioned above and human IF-B(12) and hog IF-B(12) ranged from 0.3 x 10(9) M(-1) to 13.0 x 10(9) M(-1). Apparent differences in the K(a) for human IF-B(12) and hog IF-B(12) existed in most species; (d) the number of ileal IF-B(12) binding sites per gram (wet weight) of ileal mucosa ranged from 0.3 x 10(12) to 4.9 x 10(12). The same value was always obtained with human IF-B(12) and hog IF-B(12) for any given homogenate preparation; (c) 100-fold excesses of free B(12) or human IF and hog IF devoid of B(12) did not significantly inhibit human IF-B(12) and hog IF-B(12) binding to human and hog ileal homogenates. THESE EXPERIMENTS PERFORMED WITH HOMOGENEOUS IF INDICATE THAT: (a) gastric factors other than IF are not required for B(12) binding to ileal IF-B(12)-binding sites: (b) the mechanism of ileal IF-B(12) binding is different from that of free B(12) or of B(12) bound to non-IF-B(12)-binding proteins; (c) human IF and hog IF have different structures; (d) human IF-B(12) and hog IF-B(12) bind to the same ileal binding sites; and (c) human and hog ileal IF-B(12) binding sites bind free B(12) and human and hog IF devoid of B(12) poorly, if at all.

Authors

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Pub Type(s)

Journal Article

Language

eng

PubMed ID

4201500

Citation

Hooper, D C., et al. "Characterization of Ileal Vitamin B12 Binding Using Homogeneous Human and Hog Intrinsic Factors." The Journal of Clinical Investigation, vol. 52, no. 12, 1973, pp. 3074-83.
Hooper DC, Alpers DH, Burger RL, et al. Characterization of ileal vitamin B12 Binding using homogeneous human and hog intrinsic factors. J Clin Invest. 1973;52(12):3074-83.
Hooper, D. C., Alpers, D. H., Burger, R. L., Mehlman, C. S., & Allen, R. H. (1973). Characterization of ileal vitamin B12 Binding using homogeneous human and hog intrinsic factors. The Journal of Clinical Investigation, 52(12), 3074-83.
Hooper DC, et al. Characterization of Ileal Vitamin B12 Binding Using Homogeneous Human and Hog Intrinsic Factors. J Clin Invest. 1973;52(12):3074-83. PubMed PMID: 4201500.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Characterization of ileal vitamin B12 Binding using homogeneous human and hog intrinsic factors. AU - Hooper,D C, AU - Alpers,D H, AU - Burger,R L, AU - Mehlman,C S, AU - Allen,R H, PY - 1973/12/1/pubmed PY - 1973/12/1/medline PY - 1973/12/1/entrez SP - 3074 EP - 83 JF - The Journal of clinical investigation JO - J. Clin. Invest. VL - 52 IS - 12 N2 - Elucidation of the mechanism of intrinsic factor (IF)-mediated vitamin B(12) (B(12)) binding to ileal binding sites has been hampered by the use of crude or only partially purified preparations of IF in previous studies. We have used homogeneous human IF and hog IF isolated by affinity chromatography to study [(57)Co]B(12) binding to ileal mucosal homogenates. The following observations were made: (a) Human IF-B(12) and hog IF-B(12) were bound to human, monkey, hog, dog, rabbit, mouse, hamster, and guinea pig ileal, but not jejunal, homogenates in amounts significantly greater than free B(12) or B(12) bound to five other homogeneous B(12)-binding proteins; (b) only IF-mediated B(12) binding was localized to ileal homogenates and was inhibited by EDTA; (c) values for the association constant (K(a)) for the various ileal homogenates mentioned above and human IF-B(12) and hog IF-B(12) ranged from 0.3 x 10(9) M(-1) to 13.0 x 10(9) M(-1). Apparent differences in the K(a) for human IF-B(12) and hog IF-B(12) existed in most species; (d) the number of ileal IF-B(12) binding sites per gram (wet weight) of ileal mucosa ranged from 0.3 x 10(12) to 4.9 x 10(12). The same value was always obtained with human IF-B(12) and hog IF-B(12) for any given homogenate preparation; (c) 100-fold excesses of free B(12) or human IF and hog IF devoid of B(12) did not significantly inhibit human IF-B(12) and hog IF-B(12) binding to human and hog ileal homogenates. THESE EXPERIMENTS PERFORMED WITH HOMOGENEOUS IF INDICATE THAT: (a) gastric factors other than IF are not required for B(12) binding to ileal IF-B(12)-binding sites: (b) the mechanism of ileal IF-B(12) binding is different from that of free B(12) or of B(12) bound to non-IF-B(12)-binding proteins; (c) human IF and hog IF have different structures; (d) human IF-B(12) and hog IF-B(12) bind to the same ileal binding sites; and (c) human and hog ileal IF-B(12) binding sites bind free B(12) and human and hog IF devoid of B(12) poorly, if at all. SN - 0021-9738 UR - https://www.unboundmedicine.com/medline/citation/4201500/Characterization_of_ileal_vitamin_B12_Binding_using_homogeneous_human_and_hog_intrinsic_factors_ L2 - https://doi.org/10.1172/JCI107506 DB - PRIME DP - Unbound Medicine ER -