Relationship between Iron and Phosphate in Mammalian Ferritins

Desilva, D.; Guo, Jia; Aust, Steven D.

doi:10.1006/abbi.1993.1308

Cited by 39 publications

(13 citation statements)

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“…As indicated above, CKD patients have elevated serum ferritin concentrations suggesting a possible role for ferritin as an NTBI binding protein. Also, consistent with this hypothesis are reports that ferritin has increased rates of iron loading in the presence of phosphate (Aitken-Rogers et al 2004;Orino et al 2002;Cheng and Chasteen 1991;Polanams et al 2005;de Silva et al 1993).…”

Section: Introductionsupporting

confidence: 60%

“…However, in vitro iron loading in the presence of phosphate produced cores with a 1:1 iron to phosphate ratio, which is very different than native ferritin cores (Table 2). Several groups have prepared native-like mineral cores (* 10 Fe/phosphate) in ferritin by first loading the iron and then incubating ferritin in a phosphate solution (Treffry and Harrison 1978;de Silva et al 1993). It was proposed that to obtain ferritin samples with the low phosphate contents found in vivo ferritin would be required to dock with a membrane ion transport protein to allow iron to be directly channeled into ferritin followed by phosphate deposition on the mineral surface.…”

Section: Discussionmentioning

confidence: 99%

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The ferroxidase center is essential for ferritin iron loading in the presence of phosphate and minimizes side reactions that form Fe(III)-phosphate colloids

2011

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Ferritin iron loading was studied in the presence of physiological serum phosphate concentrations (1 mM), elevated serum concentrations (2-5 mM), and intracellular phosphate concentrations (10 mM). Experiments compared iron loading into homopolymers of H and L ferritin with horse spleen ferritin. Prior to studying the reactions with ferritin, a series of control reactions were performed to study the solution chemistry of Fe(2+) and phosphate. In the absence of ferritin, phosphate catalyzed Fe(2+) oxidation and formed soluble polymeric Fe(III)-phosphate complexes. The Fe(III)-phosphate complexes were characterized by electron microscopy and atomic force microscopy, which revealed spherical nanoparticles with diameters of 10-20 nm. The soluble Fe(III)-phosphate complexes also formed as competing reactions during iron loading into ferritin. Elemental analysis on ferritin samples separated from the Fe(III)-phosphate complexes showed that as the phosphate concentration increased, the iron loading into horse ferritin decreased. The composition of the mineral that does form inside horse ferritin has a higher iron/phosphate ratio (~1:1) than ferritin purified from tissue (~10:1). Phosphate significantly inhibited iron loading into L ferritin, due to the lack of the ferroxidase center in this homopolymer. Spectrophotometric assays of iron loading into H ferritin showed identical iron loading curves in the presence of phosphate, indicating that the ferroxidase center of H ferritin efficiently competes with phosphate for the binding and oxidation of Fe(2+). Additional studies demonstrated that H ferritin ferroxidase activity could be used to oxidize Fe(2+) and facilitate the transfer of the Fe(3+) into apo transferrin in the presence of phosphate.

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Section: Introductionsupporting

confidence: 60%

Section: Discussionmentioning

confidence: 99%

The ferroxidase center is essential for ferritin iron loading in the presence of phosphate and minimizes side reactions that form Fe(III)-phosphate colloids

2011

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“…In ironloaded Phaseolus leaves the electron-dense particles represent the iron core of ferritin. It is well known that there are considerable variations in iron/phosphorus ratios of ferritin cores, ranging from nearly 2 in bacterial ferritin to 8 in horse spleen ferritin (de Silva et al, 1993;Wade et al, 1993). However, from the results discussed above, there is no evidence for ferritin depositions in the mutant leaves.…”

Section: Discussionmentioning

confidence: 89%

Subcellular Localization and Characterization of Excessive Iron in the Nicotianamine-less Tomato Mutant chloronerva

1995

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To understand the function of the Fe2+-complexing compound nicotianamine (NA) in the iron metabolism of plants we have localized iron and other elements in the NA-containing tomato wild type (Lycopersicon esculentum) and its NA-free mutant chloronerva by quantitative x-ray microanalysis. Comparison of element composition of the rhizodermal cell walls indicated that the wild type accumulated considerable amounts of iron and phosphorus in the cell wall, whereas in the mutant iron and phosphorus were detected in the cytoplasm and vacuoles of the rhizodermis. In mutant leaves containing high iron concentrations in the symplast, electron-dense inclusions were detected in chloroplasts and phloem. Such particles, consisting mainly of iron and phosphorus, were never found in the wild type and were very rarely detected in young chlorotic mutant leaves or after treatment of the mutant with NA. For further characterization the electron-dense inclusions in mutant leaves were isolated and compared by sodium dodecyl sulfate-gel electrophoresis and immunoblotting to ferritin from iron-loaded Phaseolus vulgaris leaves. Antibodies raised against purified Phaseolus leaf ferritin were used. Neither in mutant nor in wild type (iron loaded and control) was ferritin protein detected. These results suggest that the electron-dense inclusions in mutant leaves are not identical with ferritin. It is concluded that NA is necessary to complex ferrous iron in a soluble and available form within the cells. In the absence of NA the precipitation of excessive iron in the form of insoluble ferric phosphate compounds could protect the cells from iron overload.

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“…One mechanism of controlling the reactive nature of iron is to store excess iron in ferritin. Iron is stored inside ferritin as a ferric oxyhydroxide polymer associated with some phosphate (deSilva et al 1993;Granick and Hahn 1944). In order for iron to be incorporated into ferritin it must be presented as Fe(II) and subsequently oxidized to Fe(III).…”

Section: Introductionmentioning

confidence: 99%

The effect of copper deficiency on the formation of hemosiderin in sprague-dawley rats

et al. 2007

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We demonstrated previously that loading iron into ferritin via its own ferroxidase activity resulted in damage to the ferritin while ferritin loaded by ceruloplasmin, a copper-containing ferroxidase, was not damaged and had similar characteristics to native ferritin (Welch et al. (2001) Free Radic Biol Med 31:999-1006). Interestingly, it has been suggested that the formation of hemosiderin, a proposed degradation product of ferritin, is increased in animals deficient in copper. In this study, groups of rats were fed normal diets, copper deficient diets, iron supplemented diets, or copper deficient-iron supplemented diets for 60 days. Rats fed copper-deficient diets had no detectable active serum ceruloplasmin, which indicates that they were functionally copper deficient. There was a significant increase in the amount of iron in isolated hemosiderin fractions from the livers of copper-deficient rats, even more than that found in rats fed only an iron-supplemented diet. Histological analysis showed that copper-deficient rats had iron deposits (which are indicative of hemosiderin) in their hepatocytes and Kupffer cells, whereas rats fed diets sufficient in copper only had iron deposits in their Kupffer cells. Histologic evidence of iron deposition was more pronounced in rats fed diets that were deficient in copper. Additionally, sucrose density-gradient sedimentation profiles of ferritin loaded with iron in vitro via its own ferroxidase activity was found to have similarities to that of the sedimentation profile of the hemosiderin fraction from rat livers. The implications of these data for the possible mechanism of hemosiderin formation are discussed.

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Relationship between Iron and Phosphate in Mammalian Ferritins

Cited by 39 publications

References 0 publications

The ferroxidase center is essential for ferritin iron loading in the presence of phosphate and minimizes side reactions that form Fe(III)-phosphate colloids

The ferroxidase center is essential for ferritin iron loading in the presence of phosphate and minimizes side reactions that form Fe(III)-phosphate colloids

Subcellular Localization and Characterization of Excessive Iron in the Nicotianamine-less Tomato Mutant chloronerva

The effect of copper deficiency on the formation of hemosiderin in sprague-dawley rats

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