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At least 919 records · Page 51Linked to original sources
PubMed1988

Heteronuclear NMR studies of cobalamins. 31P NMR observations of cobalamins bound to a haptocorrin from chicken serum.

A vitamin B12-binding protein (haptocorrin) from chicken serum has been purified to homogeneity by photodissociative affinity chromatography and characterized by gel electrophoresis and UV-visible spectrophotometry of its aquocobalamin, hydroxocobalamin, and cyanocobalamin complexes. The haptocorrin is a glycoprotein with a molecular mass of about 70 kDa and a protein moiety of about 40 kDa. 31P NMR resonances of the haptocorrin-cobalamin complexes are relatively broad singlets (with or without proton decoupling) shifted downfield by 0.7-1.0 ppm from the position of the free cobalamin resonances. From the line width data, the relaxation of the phosphorus nucleus is found to be dominated by chemical shift anisotropy with a very minor (13%) component from dipolar interaction with the two nearest neighbor protons. The rotational correlation time of the haptocorrin at 25 degrees C is estimated to be 85 ns and the activation energy for rotational correlation 3.9 +/- 0.3 kcal mol-1. The downfield shift of the 31P resonances of cobalamins upon binding to the haptocorrin cannot be due to hydrogen bonding phosphodiester moiety or displacement of the axial base by a group on the protein. Calculations also show that the downfield shift is very unlikely to be due to dipolar deshielding of the phosphorus nucleus by the ring current of an aromatic residue of the protein. It is concluded that the downfield shift of the 31P resonance must be due to sterically induced changes in phosphodiester conformation which may, or may not, involve steric compression of the axial Co-N bond.

Algorithms↗
PubMed1986

Radioimmunoassay for assessing exocrine pancreatic insufficiency, based on the differential enzymatic degradation of cobalamin-binding proteins.

Pancreatic proteases degrade the protein moiety of the R protein-cobalamin complex but not the intrinsic factor-cobalamin complex. Accordingly, we used these two proteins as substrates in an in vitro enzymatic assay to assess pancreatic function by incubating basal jejunal fluids with a mixture of intrinsic factor and cyano[57Co]cobalamin coupled to R-type protein and then using immunoprecipitation to determine the distribution of isotopically labeled cobalamin bound to the two proteins. With normal jejunal fluids, 91.2 (SD 6.1)% and 4.5 (SD 5.5)% of cyano[57Co]cobalamin was precipitated with antisera to intrinsic factor and anti-R protein, respectively. In the patients' jejunal fluids, the cyano[57Co]cobalamin precipitated with the respective antisera was 5.3 (SD 10.0)% and 96 (SD 6.2)%. In patients with other gastrointestinal problems, the sequestration of cobalamin was indistinguishable from that observed with the normal fluids. The clearcut discrimination this radioimmunoassay provided between abnormal and normal samples was confirmed by parallel comparative chromatographic analysis.

Chromatography, Gel↗
PubMed1987

Cobalamin-binding protein in gastric juice as a new tumor marker in gastric cancer.

Cobalamin-binding protein (binder) in gastric juice was studied as a biochemical marker of gastric cancer. Fasting gastric juice of cancer patients and controls with benign disease was used for separation of cobalamin binders by gel filtration and DEAE-cellulose column chromatography. Physicochemical properties of the binder in gastric cancer patients were shown to have a larger molecular size and more acidic isoelectric point than the control binder. The binder was found in the gastric juice of all patients with early gastric cancer. Detection of the binder may be clinically valuable as a possible marker in the diagnosis of gastric cancer.

Chromatography, DEAE-Cellulose↗
PubMed1987

Immunofluorescent localization of vitamin B12-binding protein from sow's milk in the ileal mucosa of piglets.

Studies in vitro have shown that the vitamin B12-binding protein from sow's milk enhances vitamin B12 absorption by the neonatal piglet. In the present paper, localization of the milk vitamin B12 binding protein on the brush border membrane of intact ileal enterocytes was demonstrated by an immunocytochemical procedure in which the binding protein was incubated within isolated loops of ileum of anesthetized neonatal piglets.

Animals↗
PubMed1986

Rapid collection of human intrinsic factor uncontaminated with cobalophilin (R binder).

Intrinsic factor and R binder cobalamin binding capacity (CblBC) were measured in gastric juices obtained through feeding gastrostomy tubes (FG-GJ) from six patients with relatively complete obstruction to swallowing because of surgical resections for oropharyngeal or laryngeal carcinomas. Controls were six nonpernicious anemia gastric juices. In five of the six FG-GJ 97% of CblBC was intrinsic factor. In the sixth FG-GJ, with GJ pH = 7.2, in addition to intrinsic factor there was 22% nonintrinsic factor cobalamin-specific binder, which presumably represented partially degraded R binder refluxed from the duodenum. These data demonstrate that relatively "pure" intrinsic factor, i.e., uncontaminated with other cobalamin binders, can easily be obtained by simple drainage of FG-GJ. The study also supports evidence that gastric juice R binder is either swallowed or refluxed from the duodenum, and does not originate in the stomach.

Gastric Juice↗
PubMed1985

Isolation and characterization of methionine synthetase from human placenta.

The cobalamin-dependent enzyme, methionine synthetase, has been purified approximately 1000-fold to apparent homogeneity from human placenta with a 19% recovery. The final two steps of the purification utilized two different affinity columns. The first was a N5-methyltetrahydrofolate-cystamine-agarose column, and the second was a S-adenosylhomocysteine-agarose column. The enzyme was eluted from the first affinity column by buffer containing reducing agent which released the folate and the enzyme while elution from the second affinity column was accomplished with buffer containing 0.5 M sodium chloride. Criteria for purity were the observations that single peaks of enzyme activity, protein, and cobalamin with an apparent molecular weight of 160,000 were obtained by gel filtration and that holomethionine synthetase contained 1 mol of cobalamin/mol of protein. Furthermore, analysis by high performance liquid chromatography using a molecular weight sizing column demonstrated a single peak of protein with a corresponding cobalamin peak. This single peak of protein was progressively converted to a second protein peak that was enzymatically inactive, and this conversion was associated with a directly proportional loss of enzyme activity and cobalamin from the first peak. Methionine synthetase appeared to have a molecular weight of 160,000 on unreduced sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis and subunits of Mr 90,000, 45,000, and 35,000 on reduced sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis.

5-Methyltetrahydrofolate-Homocysteine S-Methyltran↗
PubMed1979

Serum vitamin B 12 and folic acid levels in patients with fasciolopsiasis.

Serum vitamin B12, serum and red cell folate concentrations and vitamin B12 absorption were studied in 100 patients with fasciolopsiasis. A mean value of serum vitamin B12 level in the patient group was found to be significantly lower than that of normal subjects and 14% of these patients had serum vitamin B12 level less than 100 pg/ml. Serum UBBC and TBBC levels in the patients were significantly higher than those of the normal subjects. Serum TCI and TCIII increased significantly while TCII decreased. Vitamin B12 absorption was found to be impaired in 3 of 9 patients studied. There was no relationship seen between serum vitamin B12 level and vitamin B12 absorption. The mean values of serum folate and red cell folate levels in the patient group were significantly lower than those of normal subjects. Fifteen of 100 patients (15%) had serum folate level less than 3 ng/ml, while all of them had red cell folate higher than 100 ng/ml. Serum folic acid binding protein levels (FABP) in these patients, were not significantly different from those of normal subjects.

Child↗
PubMed1979

The forms and transport of plasma cobalamins in normal man and in myeloproliferative states.

Seven patients with MP and four controls were injected with 0.04 to 0.05 microgram of [57Co] cyanocobalamin i.m. or i.v. in order to study the shift of binding with time and the conversion of one Cbl to another. The initial pattern of binding reflected the proportion of the apo forms of TC II and R binders. In MP there was more initial binding of the injected Cbl to R-type binders and less to TC II. During the first 48 hr after intake, the injected Cbl remained mostly as cyanocobalamin. Some adenosylcobalamin appeared transiently in both control and MP subjects. Radioactive methylcobalamin did not appear in the circulation until after 48 hr, and the conversion of cyanocobalamin to methylcobalamin within the circulation was greater in MP subjects. Serum from some subjects converted small amounts of cyanocobalamin to all other forms in vitro by a heat-stable, extracellular property which was abolished by dialysis of the serum. This property of serum could have accounted for the early conversion to adenosylcobalamin but not, at least as an in vitro phenomenon, to the late appearance of methylcobalamin. Although the expected increases and abnormal patterns of R binders were observed in MP, these abnormalities could not be correlated with the increased conversion to plasma methylcobalamin. During the first 6 hr after injection the R binder-Cbl designated as alpha 2-R-Cbl disappeared from the circulation at a rate faster than that of alpha 1-R-Cbl. Subsequently the alpha 2 and alpha 1 components of R binder-Clb cleared at the same rate, and this rate was the same for both control and MP subjects.

Carrier Proteins↗