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PubMed1979

The relative affinity of transferrin and albumin for zinc.

The relative affinity of transferrin and albumin for zinc has been measured by competitive dialysis at a low zinc concentration in 0.15 M NaCl, 50 mM HEPES, 0.1 mM trisodium citrate (pH 7.2). There were small differences between albumins and larger ones between transferrin preparations, but all albumins bound zinc more firmly than any transferrin did. It is known that transferrin is largely responsible for the uptake of zinc from an intestinal membrane in rats, but much of the metal is subsequently transferred to albumin. The current results show that both in humans and in rats (a) no special mechanism is needed to provide energy for this transfer, and (b) full equilibration would lead to virtually complete transfer in contrast with what actually occurs in vivo.

Humans↗
PubMed1980

Binding of xylenol orange to transferrin. Demonstration of metal-anion linkage.

The iron transport protein, transferrin, binds two metal ions and, concomitantly, two carboxylate anions. The metal ion indicators, xylenol orange and semi-xylenol orange are carboxylate anions which exhibit a characteristic visible spectrum when attached to a metal. We prepared the ternary complexes VO2+-transferrin-xylenol orange and VO2+-transferrin-semi-xylenol orange. The EPR spectra show that the vanadyl ion is attached to the protein and the visible spectra show that the xylenol orange or semi-xylenol orange is attached to the metal. The implication is that in other metal-transferrin-anion complexes, the anion is directly attached to the metal.

Chemical Phenomena↗
PubMed1984

Increase of transferrin receptors in regenerating rat liver cells after partial hepatectomy.

The change of transferrin receptors in regenerating rat liver cells after partial hepatectomy was demonstrated. The binding of 125I-labeled transferrin to the cells began to increase after 24 h of partial hepatectomy and reached about double that of the non-operated normal rat liver cells. A Scatchard analysis of binding parameters showed 1.62 X 10(5) (Ka: 1.04 X 10(7) M-1) in normal cells and 3.36 X 10(5) (Ka: 1.23 X 10(7) M-1) in regenerating cells. This reflected on increase of transferrin receptor number and little change occurred in the binding affinity between transferrin and its surface receptor.

Animals↗
PubMed1984

Molecular cloning and sequence analysis of cDNA for human transferrin.

A cDNA clone for human transferrin was identified from a human liver cDNA library by pre-screening with different ss-cDNA probes against length-fractionated liver mRNAs, positive hybridization-selection and nucleotide sequence analysis. The insert was of 1 kb, encoding human transferrin from aminoacid 403 through the COOH terminus, with a 3' non coding region of 166 nucleotides. This insert hybridized with a single major mRNA species of about 2.4 kb and several genomic DNA restriction fragments. Hybridization of the Southern blots with different parts of the transferrin insert and at different stringences suggest that the various bands observed correspond to splice sites inside one gene rather than to hybridization to several related genes. Finally, a single or a low number of transferrin gene copies seem to exist in the human genome.

Animals↗
PubMed1988

Perturbation of intracellular pH by DIDS on endocytosis of transferrin and iron uptake in rabbit reticulocytes.

DIDS (4,4'-diisothiocyanostilbene-2,2'-disulfonic acid) inhibited transferrin and iron uptake by rabbit reticulocytes in a dose-dependent manner. Measurement of intracellular pH shows that DIDS neutralized the pH in the intracellular vesicles and at the same time, rendered the cytoplasmic pH more acidic. The latter may be the result of a perturbance in the acid-extruding mechanism(s) by DIDS, a known anion exchange blocker. Examination of the single-cycle endocytosis of transferrin with pulse-chased technique suggests that DIDS retarded transferrin internalization, iron unloading and transferrin receptor recycling in the cells.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1995

Proton release from HeLa cells and alkalization of cytoplasm induced by diferric transferrin or ferricyanide and its inhibition by the diarylsulfonylurea antitumor drug N-(4-methylphenylsulfonyl)-N'-(4-cholorophenyl) urea (LY181984).

Proton release from HeLa cells was stimulated by an external oxidant, potassium ferricyanide, or by the growth factor diferric transferrin. This stimulated proton release was inhibited by the antitumor sulfonylurea LY181984 [N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl)urea] over the concentration range 10 nM to 1 microM. The antitumor-inactive sulfonylurea analog LY181985 [N-(4-methylphenylsulfonyl)-N'-(phenyl)urea] was without effect at 1 microM and required 10-100 microM concentrations to inhibit proton release. Diferric transferrin-induced alkalization of the cytoplasm estimated by BCECF [2',7'-bis(2-carboxyethyl)-5,(and 6)-carboxyfluorescein] fluorescence also was inhibited by 1 microM LY181984 but not by 1 microM LY181985. The inhibited component appeared to be amiloride resistant. The proton release induced by either ferricyanide or diferric transferrin was inhibited by about 35% at a near optimal amiloride concentration of 0.2 mM or at a dimethylamiloride concentration of 0.075 mM. However, the induced proton release was inhibited further by LY181984. Conversely, when proton release was inhibited fully by LY181984 at a near optimal concentration of 10 microM (50% inhibition), increasing concentrations of amiloride or dimethylamiloride resulted in additional inhibitions of 16 and 23%, respectively. However, the inhibitions by LY181984 and the amilorides were additive, suggesting that amiloride and the sulfonylureas may act independently. Evidence for an action of the sulfonylurea in inhibiting proton efflux differently from that of the amilorides came from measurements of sodium uptake either by fluorometry or by direct measurement with 22Na+. Sodium uptake was not inhibited by either LY181984 or LY181985 in HeLa cells at concentrations of LY181984 sufficient to inhibit proton efflux by 80% or more. The results show LY181984 to be a potent inhibitor of diferric transferrin- or ferricyanide-induced proton efflux and cytoplasmic alkalization in HeLa cells and that the inhibition may involve a component of proton transport that is resistant to amiloride.

Amiloride↗
PubMed1985

A study of the microheterogeneity of transferrin in cirrhotic patients.

In order to assess the specificity of transferrin molecular changes, we compared concentrations of subfractions and total transferrin in cirrhotic patients, in patients having non-alcoholic hepatitis, in patients with liver cancer, and in controls. The study was carried out in 79 patients divided into four groups: 20 patients with biopsy-proven cirrhosis of alcoholic origin, 20 patients with non-alcoholic hepatitis, 19 patients with liver cancer and 20 controls. Subfractions of serum transferrin were separated by isoelectric focusing followed by direct immunofixation. Fractions pI 5.7 percentages (expressed as percentages of one fraction over total transferrin) were significantly higher in the cirrhotic group than in the control group (p less than 0.01). Fraction pI 5.9 percentages were significantly higher in the cirrhotic group than in the hepatitis or control groups (p less than 0.05), or liver cancer group (p less than 0.01). A quantitative increase of fraction pI 5.7 was found in the cirrhotic patients. However, in this study, this parameter did not discriminate between patients with parenchymal liver diseases of alcoholic or other origin. Therefore, the value of determining fraction pI 5.7 as a marker of chronic alcohol consumption seems questionable. The elevation of fraction pI 5.9 constantly found in the cirrhotic patients could not be explained and needs further investigations.

Adult↗
PubMed1986

A preliminary study of urinary transferrin as a marker for prostatic cancer.

Traditional serum markers used in the diagnosis of prostate cancer lack sensitivity and specificity. Prostatic fluid is in direct contact with the prostate epithelium and, thus, has been investigated as a better source for potentially useful markers. Since prostatic fluid contents can enter the urine directly through the urethra, without prerequisite entry into blood, proteins present in significant quantities in prostatic fluid represent candidate markers for entry into the urine, particularly in diseases affecting the prostate epithelium, such as adenocarcinoma. High concentrations of transferrin in prostatic fluid led us to examine urine transferrin levels, using an immunoturbidimetric technique. Urine transferrin was significantly increased in 18 out of 22 patients with prostate cancer in comparison to age-matched controls. Since there was no evidence of increased transferrin excretion, we suggest that prostatic fluid is the source of transferrinuria.

Aged↗
PubMed1996

Perilymph detection by beta 2-transferrin immunoblotting assay. Application to the diagnosis of perilymphatic fistulae.

beta 2-Transferrin, the asialotransferrin, is found in cerebrospinal fluid (CSF) and inner ear perilymph, but is absent from serum and other body fluids or secretions except the aqueous humor. The detection of this asialo-fraction of the transferrin in ear fluid microsamples with an immunoblotting technique is of great interest when a perilymphatic fistula (PLF) is suspected. beta 2-Transferrin was detected on microsamples collected by syringe or on micro-collagen sponges from 30 patients undergoing ear surgery. The problem is reviewed, the technique and sample preparation are explained and the results discussed. beta 2-Transferrin detection in the ear fluid allows the identification of perilymph, except in the CSF oto- or rhinorrheal context, and is proposed as a promising test to confirm perilymphatic fistula.

Blotting, Western↗
PubMed1984

Iron uptake by Chinese hamster fibroblasts from human transferrin.

The manner of uptake or iron by Chinese hamster fibroblasts, type DON, from human transferrin was investigated by means of replacement studies, in which the cells that were incubated with 125I-labelled human transferrin were chased with non-radioactive transferrin for only a few minutes. The results did not support the reversible endocytosis hypothesis for the uptake of iron from transferrin. The uptake of iron measured as 59Fe during several cell divisions was found to be a function of time and cell number. It was found that the total uptake of iron in the harvests was directly proportional to the incubation, and that the uptake per 10(6) cells levelled off in the course of time.

Animals↗
PubMed1985

Inhibition of phosphatidylcholine synthesis does not alter uptake of transferrin by LM fibroblasts.

The receptor-mediated endocytosis of diferric transferrin by LM fibroblasts has been examined to determine if de novo synthesis of phosphatidylcholine is required for this process. To test this possibility, LM cells were allowed to internalize [125I]transferrin in the presence or absence of exogenous choline. Under conditions in which de novo synthesis of phosphatidylcholine was reduced from 51% of the total to less than 10%, the initial rate of transferrin uptake was unaffected. These data suggest that the process of receptor-mediated endocytosis of transferrin can proceed normally in the absence of de novo phosphatidylcholine synthesis.

Animals↗
PubMed1990

Expression of transferrin and vitamin D-binding protein genes in an osteogenic sarcoma cell line.

Expression of genes encoding transferrin and the vitamin D-binding protein is described in a cell line, U-2 OS, derived from a human osteogenic sarcoma. The mRNA transcripts of transferrin and vitamin D-binding protein were shown to be the lengths of those found in normal human liver. The cells synthesize and secrete the transferrin and vitamin D-binding proteins, in addition to human albumin and ceruloplasmin. The U-2 OS cells were successfully transfected with chimeric genes carrying 670 bp of the 5' regulatory sequence of the human transferrin gene fused to a reporter chloramphenicol acetyltransferase gene. These data indicate that the appropriate transcriptional factors required for expression of four plasma proteins are produced by U-2 OS nuclei and that the U-2 OS cell line will be useful for studies analyzing regulation of these genes.

Ceruloplasmin↗
PubMed1995

'Brain-type' N-glycosylation of asialo-transferrin from human cerebrospinal fluid.

Asialo-transferrin from human cerebrospinal fluid was purified to homogeneity. Investigation of the structural characteristics of its oligosaccharides support our hypothesis of 'brain-type' glycosylation of intrathecally synthesized cerebrospinal fluid proteins. For carbohydrate structural analysis, high-pH anion-exchange chromatography, methylation analysis, liquid secondary ion- and matrix-assisted laser desorption/ ionization mass spectrometry of the permethylated derivatives were used. The major structure turned out to be a complex-type agalactodiantennary oligosaccharide with bisecting N-acetylglucosamine and proximal fucose. Analysis of a second transferrin preparation containing both asialo- and sialo-transferrin revealed another major glycan species derived from the sialylated transferrin variant which is galactosylated and lacks bisecting N-acetylglucosamine and fucose.

Amino Acid Sequence↗
PubMed1990

Differential expression of transferrin receptor in duodenal mucosa in iron overload. Evidence for a site-specific defect in genetic hemochromatosis.

In genetic hemochromatosis, metabolic studies have demonstrated inappropriately increased iron absorption by cells of the duodenal mucosa. It is not clear whether this reflects an intrinsic abnormality of iron homeostasis at this site or is a consequence of a more generalized defect in cellular iron metabolism particularly involving the liver. We have previously used the expression of iron-related proteins as markers of iron homeostasis and have demonstrated normal regulation of the transferrin receptor and ferritin in the liver in this condition. In the present study we used immunohistochemical techniques to study transferrin-receptor expression in the gastrointestinal epithelium in normal subjects and patients with iron overload. In untreated genetic hemochromatosis and normal subjects, villus epithelial cells expressed receptor in the basolateral, subnuclear region. In contrast, in patients with secondary iron overload, receptor staining was absent in villus epithelial cells. The cells in the duodenal crypts showed intense staining for the transferrin receptor in all subjects investigated, a finding consistent with the known behavior of this receptor in proliferating cells. Given that body iron stores in both types of iron overload were comparable, these findings indicating a failure of down-regulation of the villus enterocyte transferrin receptor in genetic hemochromatosis may reflect the presence of a regulatory defect associated with the inability to control iron absorption in this condition.

Adult↗
PubMed1985

The dissociation of some 111In chelates in the presence of transferrin and haemoglobin studied by PAC.

The interaction of [111In]Tris-chelates with protein molecules in aqueous solution at room temperature has been studied using time-integral and time-differential PAC. Increasing amounts of apo-transferrin were added to solutions of [111In]tropolonate, -acetylacetonate, -oxinate and -oxine sulphate, and of haemoglobin to [111In]tropolonate. The transfer of 111In from chelate to protein was monitored by time-integral PAC measurements. Analysis of these data in erms of stability constants showed that with added transferrin complete dissociation of each 111In chelate occurred with increasing protein concentration, the radiolabel being sequestered by the protein molecules. Confirmation of this was provided by time-differential PAC measurements at four tropolone:transferrin relative concentrations, and in the pure systems. A value for the first stability constant of transferrin is presented. Analysis of time-integral PAC data showed that added haemoglobin did not cause complete dissociation of [111In]tropolonate, a [111In]tropolone-haemoglobin complex being formed. Time-differential PAC studies of the [111In]tropolonate:haemoglobin and [111In]haemoglobin systems at 77 K and 295 K supported this conclusion, revealing quadrupole frequencies of 14.0 +/- 0.6 MHz in [111In]haemoglobin and 9.1 +/- 1.1 MHz in the mixed system.

Drug Stability↗
PubMed1986

A simple and sensitive solid-phase radioimmunoassay for measuring the transferrin content of human biological fluids: its application to seminal plasma.

A highly sensitive and reproducible radioimmunoassay was established to detect transferrin in human fluids. By this technique, applied to seminal fluid, transferrin levels (micrograms/ml) were found in normozoospermic individuals (64.49 +/- 25.41) at level higher than in oligozoospermic (38.93 +/- 21.35), azoospermic (19.49 +/- 10.23), or vasectomized (19.61 +/- 8.95) subjects. A relationship between transferrin and spermatozoid concentration in sperm was shown. These results reinforce previous findings that seminal transferrin can be used as a reliable clinical marker of Sertoli Cell function.

Body Fluids↗
PubMed1987

Release of iron from endosomes is an early step in the transferrin cycle.

Transferrin bound to K 562 cells at 4 degrees C was internalized quickly on temperature shift to 37 degrees C. Endosomes were isolated according to two different procedures. The endosome fraction was shown to be heterogeneous and consisted of two vesicle populations, differing in density properties and iron content. Iron was partially released from endosomes to the supernatant after 3 and 5 min endocytosis. Isolated endosomes, still capable of internal acidification, did not release iron on incubation with ATP. However, endosomes did release iron on incubation with the iron chelator pyridoxal-isonicotinoyl hydrazone. Gel-filtration of solubilized endosomes demonstrated the presence of the transferrin-transferrin receptor complexes, free transferrin and free low molecular weight iron.

Adenosine Triphosphate↗
PubMed1987

Human blood-brain barrier transferrin receptor.

The kinetics of binding and endocytosis of 125I-human holotransferrin by isolated human brain capillaries was examined using this system as a model of the human blood-brain barrier (BBB). Both binding and endocytosis of the peptide by human brain capillaries was temperature-dependent and the binding was saturated by holotransferrin, but not by insulin, somatostatin, or vasopressin. Scatchard analysis of the binding reaction revealed a dissociation constant of 448 +/- 110 ng/mL (5.6 +/- 1.4 nmol/L) and a maximal binding constant (Ro) of 8.0 +/- 1.5 ng/mg protein. Thus, the affinity and capacity of the BBB transferrin receptor is within the same order of magnitude as the affinity and capacity of the BBB receptors for insulin, insulinlike growth factor-I, or insulinlike growth factor-II. The human brain capillary transferrin receptor was also detected with a mouse monoclonal antibody to the receptor using the avidin/biotin/peroxidase technique. In conclusion, these studies characterize the human BBB transferrin receptor and support the hypothesis that this receptor acts as a transport system which mediates the transcytosis of transferrin-bound iron through the brain capillary endothelial cell in man.

Adult↗