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PubMed1968

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

The precipitate which resulted when (57)CoB(12) bound to normal human gastric juice was subjected to a 15% concentration of Na(2)SO(4) contained virtually no radioactivity. However, after in vivo incubation of the gastric juice-(57)CoB(12) mixture in the distal ileum of the guinea pig, the dialyzed extract of the washed mucosa contained a fraction of (57)CoB(12) which was precipitated at 15% Na(2)SO(4). In addition, in vitro incubation of gastric juice-(57)CoB(12) with an extract of the ileal mucosa or brush border membranes also resulted in the formation of a 15% Na(2)SO(4)-insoluble fraction which contained (57)CoB(12). The formation of this (57)CoB(12)-containing insoluble fraction did not occur or was diminished by (a) addition of an excess of B(12)-free normal human gastric juice. (b) reducing the incubation pH to 2, (c) incubating the mixture at 4 degrees C, (d) pretreating the ileal extract at 56 degrees C for 30 min, (e) incubating the reaction in sodium EDTA but not calcium EDTA, (f) incubating gastric juice-(57)CoB(12) 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-(57)CoB(12) filtered through G-100 and G-200 columns in the excluded volume. When the ileal extract obtained after in vivo incubation with gastric juice-(57)CoB(12) was subjected to starch gel electrophoresis one peak of radioactivity remained at the origin and another moved anodally. Eluates of each peak reacted with anti-intrinsic factor antibody indicating that at least the immunologically reacting portion of the intrinsic factor molecule was present in two fractions with different electrophoretic mobility.These studies indicate that immunologically intact intrinsic factor can be extracted from the ileum after in vivo incubation with gastric juice-(57)CoB(12), and that a macromolecular factor is present in the distal ileal mucosa which binds intrinsic factor both in vitro and in vivo, changing its solubility and electrophoretic properties. It is suggested that this ileal binding factor is the previously postulated intestinal receptor for intrinsic factor.

Animals↗
PubMed1989

Human intrinsic factor. Its primary structure compared to the primary structure of rat intrinsic factor.

Human intrinsic factor was digested by trypsin and the resulting peptides purified by gelfiltration. Two peptides were sequenced to a total of 61 amino acid residues. Including the sequence for the N-terminal peptide and four cyanogen bromide peptides previously reported, we have now determined a total of 163 amino acid residues, that is a fraction of about 0.40 of the primary structure of human intrinsic factor. The 110 of the 163 residues known of human intrinsic factor are identical to the sequence of rat intrinsic factor.

Amino Acid Sequence↗
PubMed2004

A genetic polymorphism in the coding region of the gastric intrinsic factor gene (GIF) is associated with congenital intrinsic factor deficiency.

Congenital intrinsic factor (IF) deficiency is a disorder characterized by megaloblastic anemia due to the absence of gastric IF (GIF, GenBank NM_005142) and GIF antibodies, with probable autosomal recessive inheritance. Most of the reported patients are isolated cases without genetic studies of the parents or siblings. Complete exonic sequences were determined from the PCR products generated from genomic DNA of five affected individuals. All probands had the identical variant (g.68A>G) in the second position of the fifth codon in the coding sequence of the gene that introduces a restriction enzyme site for Msp I and predicts a change in the mature protein from glutamine(5) (CAG) to arginine(5) (CGG). Three subjects were homozygous for this base exchange and two subjects were heterozygous, one of which was apparently a compound heterozygote at positions 1 and 2 of the fifth codon ([g.67C>G] + [g.68A>G]). The other patient, heterozygous for position 2, had one heterozygous unaffected parent. Most parents were heterozygous for this base exchange, confirming the pattern of autosomal recessive inheritance for congenital IF deficiency. cDNA encoding GIF was mutated at base pair g.68 (A>G) and expressed in COS-7 cells. The apparent size, secretion rate, and sensitivity to pepsin hydrolysis of the expressed IF were similar to native IF. The allelic frequency of g.68A>G was 0.067 and 0.038 in two control populations. This sequence aberration is not the cause of the phenotype, but is associated with the genotype of congenital IF deficiency and could serve as a marker for inheritance of this disorder.

Adult↗
PubMed1989

Purification of intrinsic factor receptor from pig ileum using as affinity medium human intrinsic factor covalently bound to Sepharose.

Intrinsic factor receptor was purified from hog ileum using human intrinsic factor covalently bound to Sepharose. A yield of 49.6% and a specific activity of about 2500 pmol/mg protein were achieved. The purified receptor was very unstable: 24 h of storage or addition of sodium phosphate precipitated it. The association constant of the receptor for the cyano[57Co]cobalamin-intrinsic factor complex was estimated to be 2.1 nM-1. In native polyacrylamide gel electrophoresis it resolved in two 256 and 320 kDa bands; beta-mercaptoethanol treatment cleared it into four bands corresponding to molecular masses of 107, 81.8, 63.5 and 53.2 kDa. An additional 39.3 kDa band was considered to be an artefact due to the presence of Triton X-114. Isoelectric focusing polyacrylamide gel electrophoresis resolved the receptor into two isoproteins isoelectric at pH 4.7 and 5.1. A similar result was obtained in column electrofocusing with the 125I-iodinated receptor. The 125I-labelled receptor did not crossreact with rabbit anti-human intrinsic factor antiserum. The electrophoretic properties of the receptor purified with intrinsic factor covalently bound to Sepharose were compared to those of the receptor purified by the use of the classical cobalamin-affinity medium. It was concluded that a disassembled receptor was produced using the classical method.

Animals↗
PubMed2000

Some factors which influence intrinsic factor content and its mRNA level in the rat stomach.

Factors which regulate Intrinsic Factor (IF) content and IF mRNA level were examined with an abc-ELISA and Northern blot analysis in growing rats, and compared with pepsinogen (Pg) and in terms of the increased need for vitamin B12 (V.B12). Increases in IF content and IF mRNA level gradually occurred from day 13 after birth, whereas those of Pg and Pg mRNA started from day 16. The effects of a few related hormones on the expression of IF mRNA were examined. The injection of hydrocortisone induced IF and Pg mRNA expression in 5-d-old postnatal rats. Furthermore, adrenalectomy-induced decreases in IF content and IF mRNA level in adult male rats were recovered with hydrocortisone administration. IF content and IF mRNA level were measured in the artificially and physiologically created needs for V.B12, the first being regeneration of the liver, the V.B12 storing tissue, following partial hepatectomy, and the second pregnancy or lactation. During regeneration of the liver, increases in IF content and IF mRNA level were marked, followed by reduction toward the original level after accomplishment of regeneration. Increases in IF content and IF mRNA level were also seen in lactating rats, but no increases were obtained in pregnant rats. These results suggest that the IF content and IF mRNA level are regulated not only by corticosteroids but also by the increased need for V.B12.

Adrenalectomy↗
PubMed1980

An assay for serum vitamin-B12 and for intrinsic factor antibody type I by means of hog intrinsic factor.

A method of assay for the circulating intrinsic factor antibody type I (IFA1) and for the serum vitamin-B12 level by the use of hog intrinsic factor has been developed. The results, the sources of error being taken into consideration, are in agreement with the values obtained by the generally accepted methods of ARDEMAN--CHANARIN for IFA1 and of WIDE--KILLANDER for the serum vitamin-B12 level. Parallel with the increase in the frequency of circulating IFA1, the serum vitamin-B12 level was found to decline in normal individuals as well as in patients with atrophic gastritis or pernicious anaemia. The method is suitable for the assessment of vitamin-B12 deficiency and lends itself to screening of patients tending to pernicious anaemia.

Adult↗
PubMed1984

Isolation and characterization of two species of receptor which bind intrinsic factor.

The intrinsic factor receptor from guinea pig ilea has been characterized following purification by affinity chromatography. The purified receptor complexed to intrinsic factor-cobalamin (holo-receptor) had an anhydrous molecular weight of 680,000, a Stokes radius of 10.9 nm, and a sedimentation coefficient of 15.1 S. In contrast, unsaturated receptor (apo-receptor) resolved into distinct "large" and "small" molecular species having, respectively, (i) molecular weights of 700,000 and 350,000; (ii) Stokes radii of 11.1 and 7.06 nm; (iii) sedimentation coefficients of 15.5 S and 11.9 S; (iv) association constants for binding the intrinsic factor-cobalamin complex of 7.3 and 2.5 X 10(10) liters mol-1; and (v) two isoproteins for the larger species (pI's 4.05 and 4.80), and one isoprotein for the smaller species (pI 4.90). A rabbit anti-receptor serum gave only one precipitation line in immunodiffusion against either the large or the small receptor, and each one of these two lines fused completely with the one of two lines which formed with the purified preparation containing both receptor species. Autoradiography of the precipitin lines obtained when the receptor was coupled to intrinsic factor-cyano[57Co]cobalamin demonstrated that both species of receptor were functional. The reaction of complete immunologic identity, the similar electrical properties and similar kinetics for binding to intrinsic factor, and the observed molecular weight differences indicate that the small and large apo-receptors are chemically interrelated, and suggest that the large receptor may consist of two small functional proteins.

Animals↗
PubMed1969

Radioiodination of human intrinsic factor.

Human intrinsic factor (IF) saturated with (60)Co-labeled cyanocobalamin ((60)CoB(12)) was purified and then iodinated with (125)I to yield (125)I-labeled IF-(60)CoB(12) preparations of high specific activity. Sephadex G200 and DEAE-cellulose chromatography of the iodinated IF-(60)CoB(12) complex showed coincidence of the major (125)I and the (60)Co radioactivity peaks. During starch-gel electrophoresis (60)Co radioactivity from noniodinated and iodinated complexes migrated to the same extent while (125)I radioactivity from the iodinated complex migrated slightly further anodally than did the (60)Co radioactivity. After the iodinated complex was mixed with antibody to the IF-B(12) complex (antibody II) the (125)I and (60)Co radioactivity were: (a) precipitated in similar amounts by antiglobulin serum. (b) eluted coincidentally in the 19S region on Sephadex G200, and (c) excluded to the same extent from starch gel during electrophoresis. After equilibrium exchange of IF "blocking" antibody (antibody I) for (60)Co-vitamin B(12) on (125)I-labeled IF. (125)I radioactivity from the IF-antibody I complex: (a) was precipitated by antiglobulin serum, (b) was eluated in the 19S region on Sephadex G200 gel filtration, and (c) migrated slowly towards the anode on starch-gel electrophoresis. Urinary excretion of (60)Co radioactivity in pernicious anemia patients after oral administration of (60)Co-vitamin B(12) bound to freshly prepared (125)I-labeled IF was similar to that obtained with noniodinated intrinsic factor. These results show that iodination of IF-(60)CoB(12) complex does not markedly alter the chromatographic, electrophoretic, antigenic, or absorption-promoting properties of IF.

Antigen-Antibody Reactions↗