PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “INTRINSIC FACTOR”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources
PubMed1983

Effect of bile and bile acids on binding of intrinsic factor to cobalamin and intrinsic factor-cobalamin complex to ileal receptor.

Human bile or commercially available bile acids bind [57Co]cobalamin (Cbl) due to the presence of "R"-type binders, which are normally present in the former and present as a contaminant in the latter. The competition of these R proteins for the binding of Cbl by intrinsic factor (IF) could explain the in vivo inhibition attributed previously to the bile acids themselves. R protein seems to be involved in the inhibition of Cbl binding because protease digestion of either bile or bile acid abolishes the Cbl binding ability. Moreover, antibody to R protein abolishes the inhibition. Bile or bile acids do not have a direct effect on either purified IF or the IF-Cbl receptor molecule, even though bile acids increase the attachment of IF-[57Co]Cbl to ileal brush-border membranes. These data demonstrate two steps where components of bile could affect Cbl absorption: the binding of Cbl to IF and of IF-Cbl to its ileal receptor. It is not clear whether these in vitro phenomena are important for the normal absorption of Cbl in vivo.

Animals↗
PubMed1991

Binding assay and physicochemical characteristics of solubilized intrinsic factor receptor in ileal mucosal homogenates using phenyl-Sepharose to separate the saturated receptor from free intrinsic factor.

A radioisotopic assay was set to determine the physicochemical properties of the solubilized intrinsic factor receptor in pig mucosal extracts. In this assay, phenyl-Sepharose was used to separate the receptor-intrinsic factor-labelled cobalamin complex from the free saturated intrinsic factor. The association constant (at pH 7.4) of the receptor-intrinsic factor complex was estimated at 3.4 +/- 0.3 nM-1. Adsorption of the apo-receptor to phenyl-Sepharose allowed its binding site to be made accessible to intrinsic factor with an association constant in order of 6 nM-1. The receptor binding activity obtained with five mucosal extracts was closely correlated with that obtained by gel filtration of the intrinsic factor-receptor complex (r = 0.99). The radioisotope assay was used to detect the unsaturated receptor (apo-receptor) in sucrose density ultracentrifugation and in superose 6 gel filtration. The sedimentation coefficient was 9.5 s. The apo-receptor was eluted in three peaks in gel filtration, corresponding to the formation of oligomers. The peak of the monomer was increased in presence of EDTA. Its molecular mass was estimated at 270 kDa and its Stokes radius at 5.9 nm. It was concluded that calcium is involved in the oligomerisation of the apo-receptor.

Adsorption↗
PubMed1967

A comparison of two methods for the immunoassay of intrinsic factor.

The intrinsic factor content of 263 samples of gastric juice was determined by immunoassay using charcoal absorption and by immunoelectrophoresis on acrylamide gel. There was good correlation between the results of the two techniques and, with a few exceptions, both made it possible to predict which patients would have malabsorption of radioactive vitamin B(12). Of the two methods, immunoassay using charcoal absorption generally gave the higher readings. Further study showed that this could not be attributed to the recognized difference in the principles of the two methods but that it was more likely to be due to the dissimilarity of the experimental conditions.

Absorption↗
PubMed1980

Histamine H2 receptors and intrinsic factor secretion.

Intrinsic factor (IF) secretion in healthy male subjects was studied in response to pentagastrin stimulation with and without cimetidine, and to impromidine, a histamine H2 receptor agonist. Peak and total IF output were reduced by cimetidine, but the concentration was unchanged and the response was unaffected by administration of the compound for 1 week. The IF secretory response to impromidine was similar to that to pentagastrin. It is suggested that the acid and IF components of the parietal cell secretory response are mediated via different intracellular pathways, that histamine H2 receptors do not fulfill and obligatory role in the secretion of IF and that synthesis of IF is probably not altered by cimetidine.

Cimetidine↗
PubMed1988

Isolation and structural characterization of a cDNA clone encoding rat gastric intrinsic factor.

Rat intrinsic factor (IF) has been purified and proteolytic fragments were sequenced. A cDNA library was constructed from size-enriched gastric poly(A)+ RNA and screened for IF-positive clones by antibody and synthetic oligodeoxynucleotide probe hybridization. An IF clone was isolated and sequenced, revealing a predicted primary amino acid sequence in the coding region of 421 amino acids and a putative signal sequence of 22 amino acids. The primary translation product of IF produced in a cell-free translation system displayed cobalamin (Cbl)-binding activity without proteolytic processing or glycosylation. The amino-terminal region of IF showed significant secondary structural and hydropathic homologies with the nucleotide-binding domain in NAD-dependent oxidoreductases. Alignment of the first 80 residues of IF, following the signal peptide, demonstrated homology with the nucleotide-binding domain of cytoplasmic malate dehydrogenase. Based on these data, we propose a model of IF tertiary structure in which the Cbl-binding domain resides in the NH2-terminal half of the protein.

Amino Acid Sequence↗
PubMed1985

The use of the adipose tissue transplantation technique to demonstrate that abnormalities in the adipose tissue metabolism of genetically obese mice are due to extrinsic rather than intrinsic factors.

Adipose tissue transplantation between genetically obese mice and their lean counterparts using the kidney capsule as the transplantation site has shown that the abnormally large fat cells of obese mice normalize in size when they are placed into a 'lean' environment. Furthermore, the abnormal fatty acid composition of the white adipose tissue of obese mice (higher proportion of palmitoleic acid and lower proportion of linoleic acid compared with lean) normalizes on transplantation into a 'lean' environment. Such experiments lead us to conclude that the differences in the lipolytic and lipogenic enzymes in the adipose tissue of genetically obese mice must be due to extrinsic factors rather than factors intrinsic to the adipocyte.

Adipose Tissue↗
PubMed1995

Intrinsic factor covalently bound to Sepharose as affinity medium for the purification of a soluble intrinsic factor receptor from human urine.

We have identified a soluble receptor for intrinsic factor (IF) in human urine. The purification of this protein by affinity chromatography required a preliminary purification of IF from hog pyloric mucosal extract. This was achieved by thermolabile cobalamin-ethanol-aminohexane Sepharose affinity chromatography with a 133-fold purification, a yield of 45% and a specific binding activity of 15720 pmol/mg protein. The purified Cbl-IF complex was coupled to epoxy-Sepharose with a yield of 23.8% and a specific activity of 1.2 nmol per mol of gel. The soluble IF receptor was purified form 200 ml of urine concentrate of pregnant women. Desorption was performed at pH 5.0 and in the presence of 5 mM EDTA. The soluble IF receptor was purified 17,200-fold with a yield of 52% and a IF binding capacity of 3260 pmol per mg of protein. A single protein with a Mr of 70,000 was found in silver-stained SDS-PAGE.

Animals↗
PubMed1988

Epidermal growth factor (EGF) inhibits both intrinsic factor secretion and acid secretion in histamine-stimulated isolated gastric glands.

Epidermal growth factor (EGF) is a polypeptide present in mammalian salivary glands which has been shown to have mitogenic and gastric acid inhibitory properties in vivo. The mechanisms of action of EGF at the level of the parietal cell are not clear. In the present study, we have examined the effects of EGF on both acid and macromolecular (intrinsic factor, IF) secretion stimulated by the cyclic AMP-mediated agonist histamine using the rabbit isolated gastric gland model. Acid secretion was assessed by the accumulation of [14C]aminopyrine (AP) in glands and IF in the supernatants by the binding of [57Co]cyanocobalamin. Histamine (10(-6) to 5 x 10(-5) M) resulted in a 4-6 fold increase in [14C]AP and IF (P less than 0.05). EGF alone (10(-8) M, 10(-7) M) had no significant effect on basal [14C]AP accumulation or IF secretion (P less than 0.05). EGF (10(-7) M) significantly inhibited the histamine dose-response curve for [14C]AP and IF, but a relatively greater inhibition was observed at higher histamine concentration. These data demonstrate that EGF inhibits both acid and IF secretion in vitro at concentrations consistent with those observed in vivo. The observations further support the hypothesis that EGF may play a role in the regulation of parietal cell secretion.

Aminopyrine↗