SEARCH · PubMed Health

Results for “Transcobalamins”

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 19 recordsLinked to original sources

PubMed1977

Unsaturated and cobalamin saturated transcobalamin I and II in normal human plasma.

Insolubilized antibody against human transcobalamin I has been used as a specific and precise tool for the separation of transcobalamin I (and III) from transcobalamin II. Range and mean (in parentheses) for the unsaturated binding capacity for twenty samples are 40-190 (90) pmol/l and 220-1170 (560) pmol/l for transcobalamin I (and III) and transcobalamin II, respectively. The similar figures for the cobalamin saturated transcobalamins are 200-549 (320) pmol/l and 75-475 (160 pmol/l. On analyses of the cobalamins attached to each of the transcobalamins, it is shown that methylcobalamin accounts for most of the cobalamins attached to transcobalamin I whereas transcobalamin II carries most of the 5'-deoxyadenosylcobalamin.

Antibodies↗

PubMed1976

Increased circulating levels of transcobalamin ii in gaucher's disease.

The presence of several serum protein abnormalities in Gaucher's disease prompted a study of vitamin B12 binding proteins, in which 14 of 15 consecutive patients displayed increased circulating transcobalamin II unassociated with elevations of serum vitamin B12 or other vitamin B12 binders. Transcobalamin II levels were most significantly increased in nine patients with disease severe enough to require splenectomy (P less than 0.01), but were not correlated with liver size or levels of any other laboratory feature of Gaucher's disease studied. Splenectomy, per se, did not alter circulating transcobalamin II. Chracterization of the binder in Gaucher's disease revealed identity with normal serum transcobalamin II in acid inhibition of vitamin B12 binding, chromatographic behavior, immunologic specificity and functional integrity in vitamin B12 delivery. This observation suggests a relation between reticuloendothelial-cell activity and transcobalamin II metabolism. Elevated transcobalamin II levels may provide an additional means for diagnosis and assessment of Gaucher's disease.

Adolescent↗

PubMed1978

Porcine serum cobalophilin and transcobalamin. Identification, isolation and properties including electrofocusing patterns.

Pooled porcine serum was found to contain cobalophilin (also called transcobalamin I) and transcobalamin (also called transcobalamin II). The two proteins were harvested by batchwise absorption with vitamin B-12 covalently coupled to Sepharose, and then separated from each other either by gel filtration or using an immunoadsorbent. Both proteins were finally isolated as single proteins using a second vitamin B-12-Sepharose chromatography step. Cobalophilin and transcobalamin complexed with vitamin B-12 had molecular weights by gel filtration of 135 000 and 38 000 and by the formula of Svedberg 104 000 and 44 000, Stokes radii 4.97 nm and 2.65 nm, and sedimentation coefficients 5.39 S and 3.75 S, respectively. Electrofocusing resolved the cobalophilin complex into three main isoproteins isoelectric at pH 3.23, 3.42 and 3.69, and transcobalamin into only the main component isoelectric at a value as low as pH 3.47. Neither protein was capable of binding to the ileal intrinsic factor receptor.

Animals↗

PubMed1975

[Transcobalamins in megaloblastic anemias].

Transcobalamins are proteins which carry vitamin B12 and which are normally partly unsaturated. This study of transcobalamins was carried out in 17 subjects with megaloblastic anemia (12 true cases of pernicious anemia and 5 cases of folate deficiency). Among the latter, the transcobalamins were studied in 4 cases of pernicious anemia, before and after treatment with vitamin B12. The distribution of endogenous B12 was determined in four normal controls and two cases of pernicious anemia. This vitamin is normally distributed roughly equally between the three transcobalamins, whereas in B12 deficiency, T.C.2 is very unsaturated together with T.C.1 to a lesser degree. The latent fixation capacity of the serum is increased together with the latent fixation capacity of T.C. I and, above all, T.C. II but that of T.C. III is reduced in patients with pernicious anemia. In folate deficiency, only the latent fixation capacity of T.C. II is increased. When vitamin B12 is administered in physiological dosage, T.C. I becomes gradually saturated. In pharmacological dosage, total fixation capacity together with that of T.C. I and T.C. II become gradually reduced, but in spite of high levels of circulating B12, these proteins remain partially unsaturated. Various theories are suggested to explain the variations of these three transcobalamins in megaloblastic anemia but the problem is still unclear.

Anemia, Macrocytic↗

PubMed1975

Role of transcobalamins I, II, and III in the transfer of vitamin B12 to human bone marrow cells in vitro.

A study of the uptake of transcobalamin-bound 57Co-cyanocobalamin by suspensions of human bone marrow cells has indicated that these cells can take up vitamin B12 from all 3 transcobalamins (I, II, and III). Similar transport processes were involved in the uptake from the 3 transcobalamins; uptake was dependent on the presence of calcium ions, cellular respiration and free sulphydryl groups. These results suggest that contrary to current belief, all 3 transcobalamins play a role in the transfer of vitamin B12 to tissue cells.

Biological Transport↗

PubMed1979

Purification of human transcobalamin II-cyanocobalamin by affinity chromatography using thermolabile immobilization of cyanocobalamin.

Transcobalamin II-cyanocobalamin was isolated from Cohn fraction III of pooled human plasma by affinity chromatography on cyanocobalamin-Sepharose and some conventional separation methods. The affinity ligand cyanocobalamin was coupled to AH-Sepharose by a thermolabile linkage. The unsaturated binding protein was absorbed at 4 degrees C and eluted from the column at 37 degrees C as transcobalamin II-cyanocobalamin complex. The final preparation had a specific cyanocobalamin-binding capacity of 0.98 mol cyanocobalamin/mol transcobalamin II, the yield was 55% and the purification index amounted to 1.1 . 10(6). In dodecyl sulphate polyacrylamide gel electrophoresis one major protein band was observed at a molecular weight of 37 000 and a faint band at a molecular weight of 29 000. In polyacrylamide gel isolectric focusing the pure preparation turned out to be heterogeneous with isoelectric points ranging from pH 6.2 to 6.8, possibly by the occurrence of isoproteins.

Blood Proteins↗

PubMed1979

Distribution of endogenous cobalamin between the transcobalamins in various mammals.

1. Plasma samples from ten mammals were chromatographed on Sephadex G-200 columns and the total cobalamin content of each fraction was determined. 2. Unlike the situation in man, the bulk of the endogenous plasma cobalamin was found attached to a transcobalamin II-like protein in all ten animals. Transcobalamin 0 carried between 3 and 20% and this proportion appeared to be inversely related to the plasma total cobalamin. No endogenous cobalamin peak corresponding to transcobalamin I was detected in any species, though in the rabbit 5.3% of the plasma total cobalamin was attached to a protein of apparent molecular weight 176 000.

Animals↗

PubMed1979

Evidence for 15 genetically determined electrophoretic variants of transcobalamin II in rabbit serum.

By starch gel electrophoresis and autoradiography two classes of vitamin B12 binding proteins were detected in rabbit serum. By analogy to the nomenclature used in man, the two classes of proteins were named "transcobalamin I" (TCI) and "transcobalamin II" (TCII). Fifteen TCII phenotypes were observed, and family data indicated that they are controlled by five allelic codominant genes. The possibility that the five genes arise from the action of at least two polymorphic and closely linked structural loci is discussed.

Animals↗

PubMed1979

Inherited lack of transcobalamin II in serum and megaloblastic anaemia: a further patient.

We have studied a patient, unrelated to the patients previously described, with inherited lack of the vitamin B12 binding protein Transcobalamin II. Severe haematological abnormalities were found within a few weeks of birth and responded to treatment with both vitamin B12 and folic acid. He was maintained in partial remission with such treatment until adolescence, except for a time in early childhood when folic acid alone was given and he suffered severe neurological deterioration. A the age of 18 years he was admitted to hospital because of convulsions; the deoxyuridine suppression test showed intracellular deficiency of B12 despite a normal serum B12 and normal haemoglobin concentration. His serum failed to promote the uptake of radioactive B12 by bone marrow cells, and analysis of serum B12 binding proteins demonstrated the lack of Transcobalamin II. Treatment with injections of 1000 micrograms of B12 three times weekly corrected the abnormality shown in the deoxyuridine suppression test; following this treatment, together with changes in anticonvulsive therapy, he remains healthy without occurrence of further convulsions, and is haematologically normal.

Adult↗

PubMed1976

An improved procedure for automated Edman degradation used for determination of the N-terminal amino acid sequence of human transcobalamin I and human intrinsic factor.

An improved procedure for automated Edman degradation is presented. Three programs are described, one with double cleavage and two with single cleavage. The programs presented are characterized by a reversed delivery scheme for buffer and phenyl isothiocyanate, and by reduced cleavage times. The modified procedures applied on automated Edman degradation of the vitamin B12-binding proteins human transcobalamin I and human intrinsic factor, containing approximately 390 and 350 amino residues respectively, gave the following N-terminal amino acid sequences: Human transcobalamin I Glu-Ile-Cys-Glu-Val-Ser-Glu-Glu-Asn-Tyr-Ile-Arg-Leu-Lys-Pro-Leu-Leu-Asn-Thr-Met-Ile-Gln-Ser-Asn-Tyr-Asn-?-Gly- Human intrinsic factor Ser-Thr-Gln-Thr-Gln-Ser-Ser-Cys-Ser-Val-Pro-Ser-Ala-Gln-Glu-Pro-Leu-Val-Asn-Gly-Ile-Gln-?-Leu-Met-Glu-Thr- The background accumulation seems to be related not only to the length of the polypeptide chain being degraded, but also to the content of serine (and possibly threonine). A possible N leads to O acyl shift during the cleavage is a tentative explanation. The programs here represented lead to a significant reduction in background compared to conventional programs and allowed considerable prolongation of the degradations.

Amino Acid Sequence↗

PubMed1978

Increased concentration of transcobalamin I in a patient with metastatic carcinoma of the breast.

A patient with metastatic carcinoma of the breast and increased plasma cobalamin binding capacity (about 50 nmol/1) is described. The binding protein was identified as transcobalamin I (TCI) by DEAE cellulose ion-exchange chromatography, Sephadex G200 gel filtration and agar gel electrophoresis. Although the total plasma cobalamin concentration (about 20 nmol/1) was elevated, the patient complained of neurological symptoms in accordance with a functional vitamin B12 deficiency. Hence, an inactivation of the coenzyme is suggested by the demonstration of considerable amounts of 5'-deoxyadenosylcobalamin bound to the plasma TCI. Both urinary excretion of FIGLU and methylmalonic acid were within the reference ranges. Reported cases of increased cobalamin binding in patients with nonhaematological malignancy are reviewed. Further investigations to characterize the function of the cobalamin dependent metabolic pathways are necessary to determine the importance of the increased transcobalamin binding in these patients.

Blood Proteins↗

PubMed1978

Evidence for intestinal origin of transcobalamin II during vitamin B12 absorption.

The plasma binding of newly absorbed, radioactively labelled vitamin B12 was studied during a urinary excretion (Schilling) test. Vitamin B12, after being absorbed from the gut, enters blood attached to transcobalamin II, which seems to be derived from the ileal enterocyte. The absorbed B12 re-enters the blood stream after the transcobalamin II-B12 complex is cleared by the liver and it is then excreted into the urine during the Schilling test.

Aged↗

PubMed1976

Fractionation of serum transcobalamins on charged cellulose filters.

A simple and rapid fractionation procedure of the three transcobalamins, TCI, TCII, and TCII, of human serum was achieved by filtration through a stack of charged cellulose filters composed of one cellulose-nitrate and three DEAE-cellulose (DE-81) disks. A reaction mixture containing microliter amounts of serum was incubated with excess of 57Co B12 of high specific activity, diluted with 0.1 M sodium borate buffer (pH 8.5), and passed through the filter stack by applying vacuum. Under these conditions TCII is selectively and quantitatively adsorbed to the cellulose-nitrate filter while both TCI and TCIII adsorb to the DE-81 filters. In the second step TCIII is selectively desorbed from the latter filters by a 0.05 M monopotassium phosphate solution of pH 4.6. Using sera of different distribution of transcobalamins the data obtained were comparable to those determined by the more laborious methods employing DE-52 column chromatography combined with procedures to remove TCII.

Blood Proteins↗

PubMed1978

Detection of genetic variation with radioactive ligands. III. genetic polymorphism of transcobalamin II in human plasma.

We detected genetically determined, electrophoretic variants of vitamin B12 binding proteins, most probably transcobalamin II, in human plasma. Polymorphic variants were observed in all populations tested; the two most common alleles (of at least four detected to date) attain frequencies of greater than 40% in Caucasians and Orientals. The variants are autosomally inherited and are seen as doublets in homozygotes, and four-banded patterns, the sum of two dissimilar homozygote patterns, in heterozygotes. The technique used in this survey, polyacrylamide gel electrophoresis (PAGE) autoradiography of plasma and serum labeled in vitro with 57Co-vitamin B12 is particularly applicable to the study of trace proteins such as the transcobalamins (10(-9)M). Possible functional variation in the TC II allele products is described, and the selective significance of this worldwide polymorphism is considered.

Autoradiography↗

PubMed1979

A comparison of methods for the rapid quantitation of unsaturated transcobalamin II and the R-binding proteins.

Methods for the rapid quantitation on unsaturated transcobalamin II (TC II) and R-binders in serum following separation of these binders using a) adsorption by uncoated charcoal, b) adsorption by Quso G32, c) precipitation with ammonium sulphate, and d) acidification of serum, have been compared with the standard gel filtration technique. In serum from healthy subjects and patients with elevated R-binders, the serum acidification and Quso methods yielded results in closest agreement with those obtained by gel filtration. When TC II was markedly elevated, the recommended concentration of Quso failed to remove all TC II from serum. Both the serum acidification and Quso methods are suitable for routine use, providing that with the latter method the concentration of Quso is increased when elevated levels of TC II are anticipated, as, eg, in severe jaundice. All the rapid methods tested yielded clinically significant results in patients with myeloproliferative disorders.

Acids↗

PubMed1978

Increased unsaturated transcobalamin II in active autoimmune disease.

Measurements of transcobalamin II (T.C. II) concentrations in 26 patients with lupus erythematosus, 4 with dermatomyositis, 2 with autoimmune haemolytic anaemia, and in 40 immunosuppressed renal-transplant patients showed that T.C. II levels were raised during active phases of autoimmune disease. Changes in T.C. II levels correlated better with the clinical course of autoimmune disease than did changes in C3, the titre of antinuclear antibody, or native D.N.A.-binding capacity.

Anemia, Hemolytic, Autoimmune↗

PubMed1978

Formation of transcobalamin II--vitamin B12 complex by guinea-pig ileal mucosa in organ culture after in vivo incubation with intrinsic factor--vitamin B12.

The in vivo incubation of intrinsic factor--[57Co]vitamin B12 in an ileal loop of a guinea-pig followed by in vitro culturing of segments of the ileum for 180 min has been used to study the transepithelial transport of vitamin B12. Analysis of the solubilized supernate of mucosa following the in vivo phase demonstrated that 44% of the [57Co]vitamin B12 was bound to intrinsic factor (IF), 26% was free, and 16% was bound to transcobalamin II (TCII). Following culture, similar analysis demonstrated that 18% of the vitamin was now bound to IF, 49% was free, and 35% ws bound to TCII. In the culture medium, 54% of the [57Co]vitamin B12 was free and 37% was bound to TCII. The formation of TCII-[57Co]vitamin B12 did not occur if homogenized mucosa was incubated with free[57Co]vitamin B12, but it did form in cultures of ileal segments from animals given an excess of unlabelled vitamin to saturate all circulating TCH, and in the medium containing puromycin. Indirect immunofluorescence using chicken anti-TCII demonstrated that TCII was associated with the mucosal cells of both the ileum and jejunum. These studies demonstrate that following transepithelial flux of vitamin B12 through the ileal mucosa, the vitamin becomes coupled to TCII. This coupling requires a structurally intact mucosa and the source of the TCII appears to be the ileal mucosal cell rather than unsaturated TCII circulating in the blood.

Animals↗

PubMed1979

Transplacental transport in the rabbit of vitamin B12 bound to human transcobalamin I, II and III.

Transcobalamins I, II and III (TCI, TCII, TCIII) were purified from human serum, saturated with 57Co-vitamin B12 (57Co-B12), and injected into pregnant rabbits. Whole body retention of the 57Co-B12 averaged 91% and was similar for each of the three vitamin B12 binders. A maximum of 62% of the injected 57Co-B12 was found in fetal tissues when the vitamin was injected bound to TCII, but only 6--7% when bound to TCI or TCIII. Thus TCII is responsible for the delivery of vitamin B12 to the fetus.

Animals↗