Identification of a macromolecular factor in the ileum which binds intrinsic factor and immunologic identification of intrinsic factor in ileal extracts

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Abstract

The precipitate which resulted when 57CoB12 bound to normal human gastric juice was subjected to a 15% concentration of Na2SO4 contained virtually no radioactivity. However, after in vivo incubation of the gastric juice-57CoB12 mixture in the distal ileum of the guinea pig, the dialyzed extract of the washed mucosa contained a fraction of 57CoB12 which was precipitated at 15% Na2SO4. In addition, in vitro incubation of gastric juice-57CoB12 with an extract of the ileal mucosa or brush border membranes also resulted in the formation of a 15% Na2SO4-insoluble fraction which contained 57CoB12. The formation of this 57CoB12-containing insoluble fraction did not occur or was diminished by (a) addition of an excess of B12-free normal human gastric juice. (b) reducing the incubation pH to 2, (c) incubating the mixture at 4°C, (d) pretreating the ileal extract at 56°C for 30 min, (e) incubating the reaction in sodium EDTA but not calcium EDTA, (f) incubating gastric juice-57CoB12 with an extract of jejunal mucosa. Sephadex gel filtration was used to demonstrate that the factor in the ileal extract which reacted with the gastric juice-57CoB12 filtered through G-100 and G-200 columns in the excluded volume.

Authors

Sheldon P. Rothenberg