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PubMed1991

Latex immunoassay of transferrin in urine.

A fully automated assay based on latex particle agglutination has been developed for the determination of transferrin in urine. The assay consists of incubating urine samples for 30 min at 50 degrees C with latex particles on which an anti-transferrin antibody has been adsorbed and then quantifying the residual unagglutinated particles with an optical particle counter. The measurable concentration range is 0.5-10 micrograms/l. Intra- and interassay coefficients of variation varied from 2.1 to 11.8% and the recovery averaged 102.5% (SD 13.8). Correlation coefficients between transferrinuria and albuminuria were 0.79 in 100 healthy subjects and 0.97 in 90 subjects with established or suspected glomerular involvement. Transferrin and albumin were stable in urine over the pH range 5-9 for 24 h at 37 degrees C, or for 2 weeks at 4 degrees C or room temperature. Transferrin was, however, less stable than albumin during prolonged storage of urine at 4 degrees C. The present latex immunoassay of transferrin may also be adapted to give a turbidimetric reading in which agglutination is quantified by measuring the decrease of absorbance at 360 nm.

Adult↗
PubMed1985

Identification of transferrin as the principal neptunium-binding protein in the blood serum of rats.

The binding of 239Np(V) to blood serum components of rats was examined in vivo and in vitro. After gel filtration of the serum using a Sephacryl S-300 column, 98% of the applied activity appeared with protein fractions representing coeluted albumins and transferrin. A separation of the albumin- and transferrin-proteins by ion-exchange chromatography using DEAE-cellulose showed the 239Np being entirely bound to the iron-carrier protein transferrin. The high elution yields from the ion-exchange columns, greater than 90%, suggest that the binding may be quite strong. The binding capacity of transferrin for neptunium in vivo was found to decline when the iron level in blood serum was increased. Precipitation experiments showed that 84 +/- 2% of the 239Np was precipitated with 10% (w/v) trichloracetic acid, 77 +/- 3% with 90% ethanol but only 6 +/- 1% with saturated ammonium sulphate at pH 7.4. The available data indicate that as for plutonium, thorium, americium and curium, the iron transport protein, transferrin, may be the main carrier protein for neptunium in mammalian blood serum.

Animals↗
PubMedDate not supplied

Monoclonal antibodies (GB16, GB18, GB19, GB22) raised against human placental microvilli recognize the transferrin receptor.

GB16, GB18, GB19 and GB22 are mouse monoclonal antibodies produced against full-term human placental microvilli. These antibodies reacted predominantly with the apical surface of the syncytiotrophoblast from first-trimester and full-term placentae, and also reacted with several cell lines derived from non-haematopoietic tissues by immunofluorescence. The radioiodinated BeWo (choriocarcinoma) cell surface proteins were immunoprecipitated with these four antibodies and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. The results demonstrated that the immunoprecipitates migrated at 180 and 90 kilodaltons under non-reducing and reducing conditions, respectively. Using enzyme-linked immunosorbent assay, the antigens recognized by GB16, GB18, GB19, and GB22 were able to bind human transferrin. Immunoabsorption studies showed that these four antibodies bound to the same molecule as OKT9, an antibody to the transferrin receptor. Moreover, the reactivities of these antibodies with HL-60 (promyelocytic leukaemia) cells diminished following dimethyl sulphoxide-induced differentiation by flow cytometric analysis. These data indicate that these four antibodies recognize the transferrin receptor. By competition assay, GB18 bound to an epitope different from those recognized by GB16, GB19 and GB22. In addition, GB22 displayed significant growth inhibition against the activated lymphocytes and Daudi cells, but not against HL-60 or Jurkat cells. These data suggest that these four monoclonal anti-transferrin receptor antibodies will provide additional means to investigate the physiological roles played by the transferrin receptor.

Antibodies, Monoclonal↗
PubMed1993

The cDNA sequence of horse transferrin.

The cDNA sequence of horse transferrin was determined by sequencing clones isolated from a horse liver cDNA library and clones obtained by PCR. The 2305 bp horse transferrin cDNA sequence included part of the 5' untranslated region and extended to the poly(A) tail. It had 80% sequence identity with the human transferrin cDNA, and encoded a protein of 706 residues, including a signal sequence of 19 amino acids. The horse transferrin sequence had the duplicated structure and conserved iron binding and cysteine residues which are characteristic of the transferrin family.

Amino Acid Sequence↗
PubMed1985

The hormonal control of protein N-glycosylation in the developing rabbit mammary gland and its effect upon transferrin synthesis and secretion.

Pregnant rabbit mammary gland explants cultured with insulin, prolactin and cortisol, synthesise and secrete transferrin radiolabelled with [3H]leucine or [3H]mannose. Omission of prolactin from the culture medium inhibited the incorporation of [3H]leucine into casein but not transferrin. Total transferrin secreted under these conditions was approx. 75% of the control (+prolactin) value measured by rocket immunoelectrophoresis. Little incorporation of [3H]mannose into transferrin was seen in the absence of prolactin suggesting a lack of glycosylation of the protein. Dual label experiments with [3H]mannose and [14C]leucine confirmed this. The decreased incorporation of [3H]mannose into dolichol linked intermediates suggests a general effect on protein N-glycosylation in the absence of prolactin. Thus, while the synthesis of the polypeptide backbone of transferrin does not require prolactin its glycosylation does.

Animals↗
PubMed1987

Cellular distribution of transferrin immunoreactivity in the developing rat brain.

The cellular distribution of immunoreactive transferrin has previously been studied in adult rat brain with the conclusion that transferrin is largely confined to oligodendrocytes, although studies in the developing rodent brain indicated some staining of neurons. Detailed investigations of a wider range of ages than studied earlier have shown that in the developing rat brain, transferrin is not only present in oligodendrocytes but also in other glial cell types and in neurons and endothelial cells. The preponderant cell type which is positive for transferrin and its regional distribution are, however, related to the age of the animal except in most circumventricular organs in which strong transferrin immunoreactivity was seen throughout the developmental period studied.

Animals↗
PubMed1978

The effect of acid pH and citrate on the release and exchange of iron on rat transferrin.

The effect of acid pH and citrate on the exchange of iron between binding sites of rat transferrin has been studied. In the absence of citrate, diferric transferrin shows stepwise loss of iron atoms with the first atom of iron released at approximately pH 5.2. Citrate at physiologic concentrations (1.10(-3) M) or greater allows random iron removal at pH 6.5 or less. Iron dissociation from monoferric transferrin at acid pH, with or without citrate, is a random process. At pH 7.4, randomization of iron on transferrin takes from 3 to 6 h in the presence of millimolar concentrations of citrate. We conclude that at acid pH and in the presence of citrate concentrations likely to occur in vivo in the rat there is little scrambling of iron bound to transferrin.

Animals↗
PubMed1979

Transferrin receptors on human B and T lymphoblastoid cell lines.

Experiments demonstrating the existence of receptors for iron-saturated transferrin on both B and T lymphoblastoid cell lines of human origin are described. Binding of 125I-labeled transferrin is rapid, saturable and reversible. It can be specifically inhibited by unlabeled transferrin but not by other proteins. The number of receptors on T cell lines determined by Scatchard analysis is almost double the number on B cell lines but the binding affinities are equal. The putative transferrin receptor can be removed from the cell by the proteolytic enzymes papain and trypsin, and is re-expressed during overnight incubation at 37 degrees C. Resynthesis is inhibited by puromycin. The receptor can be solubilized by deoxycholate, and retains transferrin binding capacity when non-covalently attached to an amphipathic matrix consisting of deoxycholate-coupled poly(L-lysyl) Agarose.

B-Lymphocytes↗
PubMed1980

Iron and transferrin distribution in reticulocytes incubated with heme synthesis inhibitors.

A high level of non-heme iron (either labelled or unlabelled) in mitochondria, ferritin and low-molecular-weight pool of reticulocytes was induced by preincubation with isonicotinic acid hydrazide or penicillamine together with either 59Fe- of 56Fe-labelled transferrin. Addition of apotransferrin during reincubation of 59Fe-labelled reticulocytes was accompanied by the transfer of 59Fe from low-molecular-weight pool to transferrin, which was found in the reticulocyte cytosol both free and bound to a carrier. Similarly, when cells were reincubated with 125I-labelled transferrin, more 125I-labelled radioactivity was found, in both free and carrier-bound transferrin peaks, in reticulocytes with a high level of low-molecular-weight cold iron than in control ones. These results suggest that transferrin enters reticulocytes and takes up iron from low-molecular-weight pool.

Animals↗
PubMed1980

The interaction of transferrin with isolated hepatocytes.

Freshly isolated rat hepatocytes display abut 36700 high-affinity sites to which differic transferrin may bind with an apparent association constant of 1.62 . 10(7) l . mol-1. Uptake of iron from diferic transferrin by hepatocytes is linear with time and is accelerated at increased diferric transferrin concentrations. Apotransferrin is able to decrease net iron uptake by hepatocytes from diferric transferrin by a process not dependent on the apotransferrin concentrations used or on the rate at which the cells take up iron. Immunoprecipitation of the apotransferrin during these incubations indicate that iron is being released from the cells to apotransferrin at the same time as iron is being taken up from diferric transferrin. The simultaneous uptake and release of iron, and the insensitivity to apotransferrin concentration, suggest that the processes of iron uptake and release occur via separate mechanisms. The effect of apotransferrin on net retention of iron may be one way in which the in vivo distribution of iron between sites of storage and utilization is controlled.

Animals↗
PubMed1986

Studies on the role of transferrin and endocytosis in the uptake of Fe3+ from Fe-nitrilotriacetate by mouse duodenum.

Addition of iron-binding proteins (human serum transferrin, mouse serum transferrin, human lactoferrin) to the luminal fluid in tied-off segments of mouse intestine in vivo led to reduced 59Fe3+ absorption from 59Fe3+-nitrilotriacetate when compared to 59Fe3+-nitrilotriacetate alone. Assay of transferrin in luminal fluid from tied segments revealed only trace amounts of immunoreactivity. The levels of luminal transferrin are unaltered in chronic hypoxia where iron absorption is significantly enhanced. Studies in vitro revealed that NH4Cl, dansylcadavarine, para-chloromercuribenzoate and trinitrobenzenesulphonate have no effect on initial 59Fe3+ uptake rates from 59Fe3+-nitrilotriacetate, while N-ethylmaleimide (1 mM) caused a 40% inhibition. In vivo 59Fe3+ uptake was unaffected by preincubation of tied-off segments with colchicine (5 mM) for up to 2 h. These results suggest that receptor-mediated endocytosis of transferrin is not a significant mechanism in the uptake of luminal Fe3+ by mouse duodenum.

Animals↗
PubMed1983

Partial characterization of transferrins of some species of the family Cyprinidae.

1. Transferrins of five cyprinid fishes (Tinca tinca, Ctenopharyngodon idella, Chondrostoma nasus. Hypophthalmichthys molitrix and Aristichthys nobilis) were isolated in a pure state using Sephadex G-100, DEAE-Sephadex and SP-Sephadex. 2. All the transferrins are heterogeneous. In H. molitrix and A. nobilis the heterogeneity is caused partly, but not exclusively, by the presence of sialic acid; in the other species it is independent of sialic acid. 3. Molecular weights ranging from 69,900 (T. tinca) to 78,800 (H. molitrix) were obtained by sedimentation equilibrium ultracentrifugation. SDS-polyacrylamide gel electrophoresis with beta-mercaptoethanol indicated that the transferrins are composed of a single polypeptide chain. 4. Amino acid compositions of all species were similar, the greatest similarity being in the transferrins of H. molitrix and A. nobilis. 5. Carbohydrate was not found in transferrins of T. tinca and C. idella, but was present in A. nobilis (2.63%) and H. molitrix (5.01%). 6. Alanine was N-terminal in C. idella. No N-terminal amino acid was found in T. tinca, H. molitrix and A. nobilis.

Amino Acids↗
PubMed1985

Primate (Macaca fascicularis) transferrin: isolation and partial characterization.

The serum transferrin from the primate, Macaca fascicularis is isolated by a purification protocol consisting of ammonium sulphate precipitation and column chromatography. The hexose (galactose + mannose) content of Macaca transferrin is 4.7 mole per mole of protein. Quantitative determination of the sialic acid content shows that there are two sialic acid residues per molecule of Macaca transferrin. This conclusion is supported by the neuraminidase treatment of Macaca transferrin, in which there is a 2-step decrease in electrophoretic mobility. Monoferric Macaca transferrins with Fe3+ selectively labelled at the C- and N-terminal sites (TfFec and FeNTf) are prepared at pH 5.5 and 8.5 using ferric dinitrilotriacetate [Fe(NTA)2] chelate and ferrous ammonium sulphate, respectively.

Animals↗
PubMed1991

Whey proteins of the common brushtail possum (Trichosurus vulpecula): isolation, characterization and changes in concentration in milk during lactation of transferrin, alpha-lactalbumin and serum albumin.

1. Transferrin and serum albumin were purified from both whey and serum and alpha-lactalbumin was purified from whey from the common brushtail possum (Trichosurus vulpecula). 2. The N-terminal amino acid sequences for transferrin and serum albumin were identical for the proteins from both whey and serum and showed homologies with transferrin or serum albumin from other species. 3. N- and C-terminal regions of possum alpha-lactalbumin were also sequenced and have been compared with wallaby alpha-lactalbumin and several eutherian alpha-lactalbumins. 4. Antisera raised to each of the three proteins were species specific and Western blots further confirmed the identity of the serum and whey transferrins and serum and whey serum albumins. 5. The concentration of transferrin increased ten-fold between days 110 and 130 of lactation, whereas no significant changes in the concentration of alpha-lactalbumin could be detected after day 60.

Amino Acid Sequence↗
PubMed1989

Utilization of transferrin-bound iron by Haemophilus species of human and porcine origins.

Haemophilus influenzae and H. haemolyticus acquired iron bound to human transferrin but not to human lactoferrin, ovo- or porcine transferrins. Conversely the swine pathogens H. pleuropneumoniae and H. parasuis used iron bound only to porcine transferrin. Growth under conditions of iron deprivation induced the production of siderophores and iron-repressible outer membrane proteins in H. parainfluenzae, H. paraphrophilus and H. parasuis but not in H. influenzae, H. haemolyticus or H. pleuropneumoniae. The latter 3 Haemophilus species appear to sequester transferrin bound iron via a siderophore-independent mechanism. However, the ability to produce iron chelating compounds did not enable H. parainfluenzae or H. paraphrophilus to utilize transferrin bound iron.

Animals↗
PubMed1986

The human transferrin gene: 5' region contains conserved sequences which match the control elements regulated by heavy metals, glucocorticoids and acute phase reaction.

Transferrin is a major plasma protein that transports iron to proliferating cells throughout the body. A clone containing the 5' region of the human transferrin gene has been isolated and characterized. A 14 kb EcoRI fragment was identified that contained the first 8 exons of the transferrin gene and 3.6 kb of its 5' flanking region. Conserved sequences identical or homologous to regulatory elements responding to heavy metals, glucocorticoid receptor and a putative acute phase reaction signal were identified in the 5'flanking region and intron 1. Also, the regulatory region of the transferrin gene contains a 14-bp sequence which closely matches sequences found in the interleukin-2 and gamma-interferon genes. All three genes are expressed by T lymphocytes before proliferation. A secondary loop structure similar to that proposed for the ovotransferrin gene can be formed by sequences in the 5' untranslated region of the transferrin mRNA.

Animals↗
PubMed1996

Retinol-binding protein and transferrin in urine. New markers of renal function in essential hypertension and white coat hypertension?

We studied the 24 h urinary excretion of albumin, transferrin, immunoglobulin G, and retinol-binding protein in individuals with essential hypertension, white coat hypertension, and normotension. In 56 individuals, we measured the 24 h ambulatory blood pressure (AMBP). The individuals could be divided into three groups: 26 hypertensives, 14 white coat hypertensives, and 16 normotensives. Daytime AMBP values were (median values with range in parentheses, mm Hg): hypertensives 158/105 (198 to 121/95 to 120), white coat hypertensives 141/83 (161 to 129/72 to 90), and normotensives 123/75 (148 to 102/63 to 86). We determined with immunochemical methods the 24 h urinary excretions of albumin, transferrin, and immunoglobulin G, all markers of glomerular dysfunction, and retinol-binding protein, a marker of impaired proximal tubular function. We found a significantly higher excretion of albumin and transferrin in hypertensives (P < .0000/P < .0001) and in white coat hypertensives (P < .003/P < .02) compared to normotensives. Out of 26 hypertensives, seven had microalbuminuria (> or = 30 to < 300 mg albumin/ 24 h). Two cases of microalbuminuria were found among the 14 white coat hypertensives. Immunoglobulin G excretion was not significantly increased in any of the hypertensive groups. Retinol-binding protein excretion was significantly higher in hypertensive patients (P < .007), whereas no elevation was observed in persons with white coat hypertension. In hypertensives, a significant correlation was found between urinary excretion of albumin and transferrin and office blood pressure and systolic AMBP. There was no significant correlation between the urinary excretions of IgG and retinol-binding protein and blood pressures in any of the three groups. Our findings indicate that patients with white coat hypertension, like hypertensives, have a selective type of glomerular dysfunction. However, proximal tubular dysfunction was seen only in hypertensives. Urinary excretions of albumin, transferrin, and retinol-binding protein may be useful as markers of glomerular and tubular dysfunction in essential hypertension.

Biomarkers↗
PubMed2004

Tertiary structural changes associated with iron binding and release in hen serum transferrin: a crystallographic and spectroscopic study.

The iron binding and release of serum transferrin are pH-dependent and accompanied by a conformational change between the iron-bound (holo-) and iron-free (apo-) forms. We have determined the crystal structure of apo-hen serum transferrin (hAST) at 3.5A resolution, which is the first reported structure to date of any full molecule of an apo-serum transferrin and studied its pH-dependent iron release by UV-vis absorption and near UV-CD spectroscopy. The crystal structure of hAST shows that both the lobes adopt an open conformation and the relative orientations of the domains are different from those of apo-human serum transferrin and human apolactoferrin but similar to that of hen apo-ovotransferrin. Spectroscopic analysis reveals that in hen serum transferrin, release of the first iron starts at a pH approximately 6.5 and continues over a broad pH range (6.5-5.2). The complete release of the iron, however, occurs at pH approximately 4.0. The near UV-CD spectra show alterations in the microenvironment of the aromatic residues surrounding the iron-binding sites.

Animals↗