Iron absorption and biliary excretion of transferrin in rats

Schümann, Klaus; Schäfer, S. G.; Förth, W.

doi:10.1007/bf01852047

Cited by 19 publications

(4 citation statements)

References 13 publications

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“…However, recent observations have suggested that such a mechanism seems unlikely to be at work in enterocytes. The main challenges are about the origin of the so-called "mucosal" transferrin (Schumann et al, 1986;Idzerda et al, 1986) and the occurrence of the transferrin receptor on the brush border (Parmley et al, 1985;Banerjee et al, 1986). Moreover, several lines of evidence have suggested the iron transporter role of lactotransferrin as it was postulated by In fact, the bioavailability of human milk iron is unusually high, and the incidence of iron deficiency in breast-fed infants is extremely low (Saarinen et al, 1977), coincident with the much higher lactotransferrin content in human milk as compared with cow's milk.…”

Section: Discussionmentioning

confidence: 99%

Isolation and partial characterization of a lactotransferrin receptor from mouse intestinal brush-border

Hu¹,

Mazurier²,

Montreuil³

et al. 1990

Biochemistry

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Several lines of evidence have recently suggested the occurrence of a specific lactotransferrin receptor in the small intestinal brush-border membrane in several animal species, which is thought to be involved in lactotransferrin-mediated intestinal iron absorption. We report here for the first time the isolation and partial characterization of this receptor from mouse intestinal brush border. The receptor has been purified to homogeneity by affinity chromatography on an immobilized human lactotransferrin column. The purified receptor was found to be active in that it binds iron-free and iron-saturated lactotransferrin with a Kd of 0.1 microM. Anti-receptor antibodies were prepared, and the receptor was further isolated by immunoaffinity chromatography in higher yield but in a denatured form. The purified receptor was revealed by sodium dodecyl sulfate-polyacrylamide electrophoresis to be a protein of about Mr = 130,000, consisting of a single polypeptide chain. The isoelectric point was determined to be 5.8. The receptor was further shown to bear concanavalin A and phytohemagglutinin L binding glycans. Digestion by N-glycanase and endo-N-acetyl-beta-D-glucosaminidase B led to a decrease of Mr = 25,000, while the endo-N-acetyl-beta-D-glucosaminidase H was uneffective, suggesting that the lactotransferrin receptor is mainly glycosylated by bi- and triantennary glycans. To gain further insight into the interaction of the receptor with lactotransferrin, namely, the number of ligand molecules bound per molecule of receptor, mouse lactotransferrin was cross-linked to its membrane-bound enterocyte receptor by use of radiolabeled sulfosuccinimidyl 3-[[2-(p-azidosalicylamido)ethyl]dithio]propionate (SASD).(ABSTRACT TRUNCATED AT 250 WORDS)

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Section: Discussionmentioning

confidence: 99%

Isolation and partial characterization of a lactotransferrin receptor from mouse intestinal brush-border

Hu¹,

Mazurier²,

Montreuil³

et al. 1990

Biochemistry

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“…Quantitative considerations of the bile's transferrin and iron content as well as the ratio between transferrin and albumin in the bile, however, do not support a concept in which the bile transferrin plays a major role in the absorption of food iron [21]. Since the synthesis of transferrin in the mucosa is very small or non-existent the most likely origin left for the bulk of intestinal transferrin content is the plasma.…”

Section: Discussionmentioning

confidence: 84%

“…A leading role in this process was attributed to the mucosal transferrin content [7]. In an attempt to conceptualize possible modes of interaction between transferrin and iron during intestinal iron absorption, we focused our interest in earlier studies on the origin and location of transferrin in the intestinal mucosa [19][20][21]. The findings of these studies brought evidence for an extracellular location of the bulk of mucosal transferrin.…”

Section: Introductionmentioning

confidence: 99%

On the origin of intestinal transferrin

1988

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The incorporation of 35S-L-methionine (35S-Met) into TCA-precipitable protein is used to measure protein synthesis in isolated non-vascular perfused jejunal segments and in isolated liver cells under steady-state conditions in rats. 10(5) X g supernatants of homogenates from jejunal segments and from liver cells as well as the jejunal absorbate were processed immuno-electrophoretically. Incorporation of 35S-Met radioactivity into precipitin lines with sera against transferrin, IgG and plasma proteins were autoradiographed and compared semiquantitatively with each other. Calculated on a wet-weight basis this system is sensitive enough to detect transferrin synthesis down to a level of 1% of that in the liver. Still, no transferrin synthesis was found in the jejunal mucosa, while 35S-Met incorporation into TCA precipitates and into IgG continued in isolated jejunal segments for over 2 h. A good correlation was found (r = 0.88, P less than 0.01) between mucosal and plasma transferrin in normal as well as in iron deficient rats. A complete immunologic cross-reactivity could be demonstrated between different plasma transferrins and the transferrin in three different preparations of the intestinal mucosa. Immunoblots of electropherograms after isoelectric focussing showed no distinct differences between transferrin in the plasma, bile, and in the mucosal epithelium.

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“…Fe-binding proteins are also present in the bile. Transferrin and lactoferrin translocate from the blood to the bile ( 13 , 14 , 15 ). Ferritin is present in the bile and originates from lysosomal exocytosis by hepatocytes ( 16 , 17 , 18 , 19 , 20 , 21 ).…”

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confidence: 99%

Biliary excretion of excess iron in mice requires hepatocyte iron import by Slc39a14

Prajapati

Conboy

Hojyo

et al. 2021

Journal of Biological Chemistry

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Iron is essential for erythropoiesis and other biological processes, but is toxic in excess. Dietary absorption of iron is a highly regulated process and is a major determinant of body iron levels. Iron excretion, however, is considered a passive, unregulated process, and the underlying pathways are unknown. Here we investigated the role of metal transporters SLC39A14 and SLC30A10 in biliary iron excretion. While SLC39A14 imports manganese into the liver and other organs under physiological conditions, it imports iron under conditions of iron excess. SLC30A10 exports manganese from hepatocytes into the bile. We hypothesized that biliary excretion of excess iron would be impaired by SLC39A14 and SLC30A10 deficiency. We therefore analyzed biliary iron excretion in Slc39a14 -and Slc30a10 -deficient mice raised on iron-sufficient and -rich diets. Bile was collected surgically from the mice, then analyzed with nonheme iron assays, mass spectrometry, ELISAs, and an electrophoretic assay for iron-loaded ferritin. Our results support a model in which biliary excretion of excess iron requires iron import into hepatocytes by SLC39A14, followed by iron export into the bile predominantly as ferritin, with iron export occurring independently of SLC30A10. To our knowledge, this is the first report of a molecular determinant of mammalian iron excretion and can serve as basis for future investigations into mechanisms of iron excretion and relevance to iron homeostasis.

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Iron absorption and biliary excretion of transferrin in rats

Cited by 19 publications

References 13 publications

Isolation and partial characterization of a lactotransferrin receptor from mouse intestinal brush-border

Isolation and partial characterization of a lactotransferrin receptor from mouse intestinal brush-border

On the origin of intestinal transferrin

Biliary excretion of excess iron in mice requires hepatocyte iron import by Slc39a14

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