Defining metal ion inhibitor interactions with recombinant human H- and L-chain ferritins and site-directed variants: an isothermal titration calorimetry study

Zinc and terbium, inhibitors of iron incorporation in the ferritins, have been used for many years as probes of structure-function relationships in these proteins. Isothermal titration calorimetric and kinetic measurements of Zn(II) and Tb(III) binding and inhibition of Fe(II) oxidation were used to identify and characterize thermodynamically ( n, K, Delta H degrees, Delta S degrees, and Delta G degrees ) the functionally important binding sites for these metal ions in recombinant human H-chain, L-chain, and H-chain site-directed variant ferritins. The data reveal at least two classes of binding sites for both Zn(II) and Tb(III) in human H-chain ferritin: one strong, corresponding to binding of one metal ion in each of the eight three-fold channels, and the other weak, involving binding at the ferroxidase and nucleation sites of the protein as well as at other weak unidentified binding sites. Zn(II) and Tb(III) binding to recombinant L-chain ferritin showed similar stoichiometries for the strong binding sites within the channels, but fewer weaker binding sites when compared to the H-chain protein. The kinetics and binding data indicate that the binding of Zn(II) and Tb(III) in the three-fold channels, which is the main pathway of iron(II) entry in ferritin, blocks the access of most of the iron to the ferroxidase sites on the interior of the protein, accounting for the strong inhibition by these metal ions of the oxidative deposition of iron in ferritin.

Multiple pathways for mineral core formation in mammalian apoferritin. The role of hydrogen peroxide

Human ferritins sequester and store iron as a stable FeOOH((s)) mineral core within a protein shell assembled from 24 subunits of two types, H and L. Core mineralization in recombinant H- and L-subunit homopolymer and heteropolymer ferritins and several site-directed H-subunit variants was investigated to determine the iron oxidation/hydrolysis chemistry as a function of iron flux into the protein. Stopped-flow absorption spectrometry, UV spectrometry, and electrode oximetry revealed that the mineral core forms by at least three pathways, not two as previously thought. They correspond to the ferroxidase, mineral surface, and the Fe(II) + H2O2 detoxification reactions, respectively: [see reactions]. The H-subunit catalyzed ferroxidase reaction 1 occurs at all levels of iron loading of the protein but decreases with increasing iron added (48-800 Fe(II)/protein). Reaction 2 is the dominant reaction at 800 Fe(II)/protein, whereas reaction 3 occurs largely at intermediate iron loadings of 100-500 Fe(II)/protein. Some of the H2O2 produced in reaction 1 is consumed in the detoxification reaction 3; the 2/1 Fe(II)/H2O2 stoichiometry of reaction 3 minimizes hydroxyl radical production during mineralization. Human L-chain ferritin and H-chain variants lacking functional nucleation and/or ferroxidase sites deposit their iron largely through the mineral surface reaction 2. H2O2 is shown to be an intermediate product of dioxygen reduction in L-chain as well as in H-chain and H-chain variant ferritins.

Mitochondrial ferritin expression in erythroid cells from patients with sideroblastic anemia

The sideroblastic anemias are characterized by ring sideroblasts, that is, red cell precursors with mitochondrial iron accumulation. We therefore studied the expression of mitochondrial ferritin (MtF) in these conditions. Erythroid cells from 13 patients with refractory anemia with ring sideroblasts (RARS) and 3 patients with X-linked sideroblastic anemia (XLSA) were analyzed for the distribution of cytoplasmic H ferritin (HF) and MtF using immunocytochemical methods. We also studied 11 healthy controls, 5 patients with refractory anemia without ring sideroblasts (RA), and 7 patients with RA with excess of blasts (RAEB). About one fourth of normal immature red cells, mostly proerythroblasts and basophilic erythroblasts, showed diffuse cytoplasmic positivity for HF, but very few were positive for MtF (0%-10%). Similar patterns were found in anemic patients without ring sideroblasts. In contrast, many erythroblasts from patients with sideroblastic anemia (82%-90% in XLSA and 36%-84% in RARS) were positive for MtF, which regularly appeared as granules ringing the nucleus. Double immunocytochemical staining confirmed the different cellular distribution of HF and MtF. There was a highly significant relationship between the percentage of MtF(+) erythroblasts and that of ring sideroblasts (Spearman R = 0.90; P <.0001). Reverse transcription-polymerase chain reaction studies demonstrated the presence of MtF mRNA in circulating reticulocytes of 2 patients with XLSA but not in controls. These findings suggest that most of the iron deposited in perinuclear mitochondria of ring sideroblasts is present in the form of MtF and that this latter might be a specific marker of sideroblastic anemia.

Role of iron and ferritin in TNFalpha-induced apoptosis in HeLa cells

We found that tumor necrosis factor alpha (TNFalpha)-induced apoptosis in HeLa cells was accompanied by a approximately 2-fold increase in H- and L-ferritin and a decrease in transferrin receptor, two indices of increased iron availability. Iron supplementation and overexpression of H-ferritin or its mutant with an inactivated ferroxidase center reduced by about approximately 50% the number of apoptotic cells after TNFalpha-treatment, while overexpression of L-ferritin was ineffective. The data indicate that H-ferritin has an anti-apoptotic activity unrelated to its ferroxidase activity and to its capacity to modify cellular iron metabolism.

Sensitivity of ultrasound screening for congenital anomalies in unselected pregnancies

OBJECTIVE

To assess the influence of heart defect frequency and severity on screening sensitivity of the entire spectrum of congenital anomalies (CA) and on detection rate of congenital heart defect (CHD) when performing routine ultrasound screening in unselected pregnant women.

STUDY DESIGN

Secondary analysis was performed on data from Eurofetus, a large international collaborative study of ultrasound screening for CA in unselected populations. The present study addressed the relations (i) between the frequency of CHD in the screened population and the global sensitivity of ultrasound in detecting CA; (ii) between frequency of ventricular septum defect (VSD) and detection rate of CA and CHD; and (iii) between seriousness of CHD and CHD sensitivity.

RESULTS

A negative correlation (p<0.001) between CHD frequency and CA sensitivity was observed in this study. Likewise, a negative correlation was also found between frequency of VSD and sensitivity for CA or CHD detection (p<0.001). In addition, a positive significant relationship (p<0.001) was observed between sensitivity and severity of CHD.

CONCLUSION

A low CHD frequency introduces bias in CA and CHD sensitivity evaluation. Incomplete assessment of fetal and neonatal malformations brings on systematic error, leading to the pre-eminence of severe defects in the studied population sample and artificially improving sensitivity figures. On the other hand, from a clinician's viewpoint, the higher sensitivity for severe defect is welcomed, since their detection is most crucial for appropriate management.

Mitochondrial ferritin: a new player in iron metabolism

Mitochondrial ferritin (MtF) is a novel H-type ferritin encoded by an intronless gene on chromosome 5q23.1. The protein is synthesized as a precursor of about 30 kDa that is targeted to mitochondria by a leader sequence of 60 amino acids. This leader is proteolytically removed inside the mitochondria and the resulting 22 kDa subunit forms typical ferritin shells. These shells have ferroxidase activity and are therefore likely to sequester potentially harmful free iron. However, this may be a limited function since MtF has a very restricted tissue expression. High amounts are found in testis but only very low levels are found in iron storage organs. The levels of MtF appear to correlate more with mitochondrial abundance than with iron metabolism. MtF does not seem to be an obligatory intermediate in transfer of free iron to heme and other iron compounds in mitochondria. However, its level increases dramatically in sideroblastic anemia when heme synthesis is disrupted. This increased synthesis does not appear to involve the classical translational control since MtF mRNA lacks an apparent iron response element. In transfected HeLa cells added iron is incorporated as quickly into MtF as into cytosolic ferritin. In addition, increased levels of MtF cause a redistribution of iron from cytosol to mitochondria and this effect is enhanced by iron chelation. Thus high levels of MtF result in an iron deficient phenotype in cytosol with decreased expression of ferritin and increased expression of transferrin receptor. This avidity for iron may explain why MtF levels are maintained at low levels in most normal cells. The regulation of MtF expression and possible therapeutic applications of MtF in neurological disorders involving increased iron deposition are topics for future research.

Genetic hyperferritinaemia and reticuloendothelial iron overload associated with a three base pair deletion in the coding region of the ferroportin gene (SLC11A3)

Iron overload may predominantly involve parenchymal or reticuloendothelial cells, the prototype of parenchymal iron overload being HFE-related genetic haemochromatosis. We studied a family with autosomal dominant hyperferritinaemia in whom the proband showed selective iron accumulation in the Kupffer cells on liver biopsy. Analysis of L and H ferritin genes excluded mutations responsible for hereditary hyperferritinaemia/cataract syndrome or similar translational disorders. Sequence analysis of the ferroportin gene (SLC11A3) in four individuals with hyperferritinaemia singled out a three base pair deletion in a region that contains four TTG repeats. This mutation removes a TTG unit from 780 to 791, and predicts the loss of one of three sequential valine residues 160-162. Denaturing high performance liquid chromatography can be used for its detection. SLC11A3 polymorphism analysis indicates that this probably represents a recurrent mutation due to slippage mispairing. Affected individuals may show marginally low serum iron and transferrin saturation, and young women may have marginally low haemoglobin concentration levels. Serum ferritin levels are directly related to age, but are 10-20 times higher than normal. Heterozygosity for the ferroportin Val 162 deletion represents the prototype of selective reticuloendothelial iron overload, and should be taken into account in the differential diagnosis of hereditary or congenital hyperferritinaemias.

Fever of unknown origin in the elderly

Fever of unknown origin (FUO) means fever that does not resolve itself in the period expected for self-limited infection and whose cause cannot be ascertained despite considerable diagnostic efforts. The differential diagnosis is often different in older patients, and presentation of disease is frequently nonspecific and symptoms are difficult to interpret. Multisystem disease has emerged as the most frequent cause of FUO in the elderly, and temporal arteritis is the most frequent specific diagnosis. Infections, particular tuberculosis, remain an important group. FUO is often associated with treatable conditions in this age group. Early recognition and prompt initiation of appropriate empirical therapy are cornerstones of the strategy.

Ferritin, iron homeostasis, and oxidative damage

Ferritin is one of the major proteins of iron metabolism. It is almost ubiquitous and tightly regulated by the metal. Biochemical and structural properties of the ferritins are largely conserved from bacteria to man, although the role in the regulation of iron trafficking varies in the different organisms. Recent studies have clarified some of the major aspects of the reaction between iron and ferritin, which results in the formation of the iron core and production of hydrogen peroxide. The characterization of cellular models in which ferritin expression is modulated has shown that the ferroxidase catalytic site on the H-chain has a central role in regulating iron availability. In turn, this has secondary effects on a number of cellular activities, which include proliferation and resistance to oxidative damage. Moreover, the response to apoptotic stimuli is affected by H-ferritin expression. Altered ferritin L-chain expression has been found in at least two types of genetic disorders, although its role in the determination of the pathology has not been fully clarified. The recent discovery of a new ferritin specific for the mitochondria, which is functionally similar to the H-ferritin, opens new perspectives in the study of the relationships between iron, oxidative damage and free radicals.

Human mitochondrial ferritin expressed in HeLa cells incorporates iron and affects cellular iron metabolism

Mitochondrial ferritin (MtF) is a newly identified ferritin encoded by an intronless gene on chromosome 5q23.1. The mature recombinant MtF has a ferroxidase center and binds iron in vitro similarly to H-ferritin. To explore the structural and functional aspects of MtF, we expressed the following forms in HeLa cells: the MtF precursor (approximately 28 kDa), a mutant MtF precursor with a mutated ferroxidase center, a truncated MtF lacking the approximately 6-kDa mitochondrial leader sequence, and a chimeric H-ferritin with this leader sequence. The experiments show that all constructs with the leader sequence were processed into approximately 22-kDa subunits that assembled into multimeric shells electrophoretically distinct from the cytosolic ferritins. Mature MtF was found in the matrix of mitochondria, where it is a homopolymer. The wild type MtF and the mitochondrially targeted H-ferritin both incorporated the (55)Fe label in vivo. The mutant MtF with an inactivated ferroxidase center did not take up iron, nor did the truncated MtF expressed transiently in cytoplasm. Increased levels of MtF both in transient and in stable transfectants resulted in a greater retention of iron as MtF in mitochondria, a decrease in the levels of cytosolic ferritins, and up-regulation of transferrin receptor. Neither effect occurred with the mutant MtF with the inactivated ferroxidase center. Our results indicate that exogenous iron is as available to mitochondrial ferritin as it is to cytosolic ferritins and that the level of MtF expression may have profound consequences for cellular iron homeostasis.

A novel deletion of the L-ferritin iron-responsive element responsible for severe hereditary hyperferritinaemia-cataract syndrome

In the last few years, mutations that cause disease through increased efficiency of mRNA translation have been discovered. Hereditary hyperferritinaemia-cataract syndrome (HHCS) arises from various point mutations or deletions within the iron-responsive element (IRE) in the 5'-UTR of the L-ferritin mRNA. Each unique mutation confers a characteristic degree of hyperferritinaemia and severity of cataract in affected individuals. We report a novel six-nucleotide deletion identified in an Italian family presenting with elevated serum ferritin and early onset bilateral cataract. This deletion involves a sequence with a TCT repetition and may have occurred through a mechanism of slippage mispairing. Because of the above repetition, the observed mutation can be interpreted as deletion 22-27, 23-28, 24-29 or 25-30. Structural modelling predicted an IRE stem modification that is expected to markedly reduce the binding to iron-regulatory proteins. A double-gradient denaturing gradient gel electrophoresis (DG-DGGE) method easily detected the above deletion.

Clinical, biochemical and molecular findings in a series of families with hereditary hyperferritinaemia-cataract syndrome

Hereditary hyperferritinaemia-cataract syndrome (HHCS) is an autosomal dominant disease caused by mutations in the iron responsive element (IRE) of the l-ferritin gene. Despite the elucidation of the genetic basis, the overall clinical spectrum of HHCS has been less well studied as, to date, only individual case reports have been described. Therefore, we studied a total of 62 patients in 14 unrelated families, with nine different mutations. No relevant symptoms other than visual impairment were found to be associated with the syndrome. A marked phenotypic variability was observed, particularly with regard to ocular involvement (i.e. age range at which cataract was diagnosed in 16 subjects with the C39T: 6-40 years). Similarly, serum ferritin levels varied substantially also within subjects sharing the same mutation (i.e. range for the A40G: 700-2412 microg/l). We followed an HHCS newborn in whom well-defined lens opacities were not detectable either at birth or at 1 year. The lens ferritin content was analysed in two subjects who underwent cataract surgery at different ages, with different cataract morphology. Values were similar and about 1500-fold higher than in controls. These observations suggest that: (i) in HHCS the cataract is not necessarily congenital; (ii) in addition to the IRE genotype, other genetic or environmental factors may modulate the phenotype, especially the severity of the cataract.

A human mitochondrial ferritin encoded by an intronless gene

Ferritin is a ubiquitous protein that plays a critical role in regulating intracellular iron homoeostasis by storing iron inside its multimeric shell. It also plays an important role in detoxifying potentially harmful free ferrous iron to the less soluble ferric iron by virtue of the ferroxidase activity of the H subunit. Although excess iron is stored primarily in cytoplasm, most of the metabolically active iron in cells is processed in mitochondria. Little is yet known of how these organelles regulate iron homeostasis and toxicity. Here we report an unusual intronless gene on chromosome 5q23.1 that encodes a 242-amino acid precursor of a ferritin H-like protein. This 30-kDa protein is targeted to mitochondria and processed to a 22-kDa subunit that assembles into typical ferritin shells and has ferroxidase activity. Immunohistochemical analysis showed that it accumulates in high amounts in iron-loaded mitochondria of erythroblasts of subjects with impaired heme synthesis. This new ferritin may play an important role in the regulation of mitochondrial iron homeostasis and heme synthesis.

Personal experience of the treatment of ruptured aortic aneurysms. The prognostic evaluation of some parameters

BACKGROUND

The rupture of an aortic aneurysm is the most frequent and most severe complication, with an incidence of approximately 20-40/100,000 persons each year. The aim of this study was to identify the preoperative, intraoperative and postoperative factors that may influence the mortality rate.

METHODS

Between January 1996 and December 1999 145 patients underwent emergency abdominal aortic repair surgery. One hundred and twenty-three patients represented a ruptured AAA and 22 a fissured aneurysm. One hundred and thirty-one patients were males and 14 were females; their mean age was 75+/-5.06 years. We selected a number of parameters after a review of the international literature and these were analysed in the two classes of survivors. No statistical analyses were performed on fissured aneurysms owing to the scant number of cases examined.

RESULTS

Mortality was 41.4% (44.7% in ruptured aneurysms alone). The following were negative preoperative prognostic factors: old age, hypertension, ASA V, intraoperative anuria and platelet count <100,000. Intraoperative factors included: hypotension, cardiac arrest, onset of anuria, aortic clamping in more than one site, duration of surgery, quantity of RBC and plasma transfused. The main postoperative variables correlated to mortality were: hypotension, hypothermia, onset of anuria, need for further transfusions, high creatinine levels.

CONCLUSIONS

Rapid intervention can minimise mortality in structures with expert teams of surgeons and anesthetists experienced in treating this type of pathology.

Double-Gradient Denaturing Gradient Gel Electrophoresis Assay for Identification of L-Ferritin Iron-responsive Element Mutations Responsible for Hereditary Hyperferritinemia-Cataract Syndrome: Identification of the New Mutation C14G

Background: Hereditary hyperferritinemia-cataract syndrome is an autosomic dominant disorder caused by heterogeneous mutations on the iron-responsive element (IRE) of ferritin L-chain mRNA. The mutations described to date were identified by direct sequencing of DNA from probands with hyperferritinemia often associated to bilateral cataracts. A direct genetic approach on a large population is useful to recognize polymorphisms in the DNA region and the prevalence of mutations associated with minor increases in serum ferritin and subclinical cataracts. We developed a rapid DNA scanning technique to detect mutations in a single electrophoretic analysis.

Methods: The double-gradient denaturing gradient gel electrophoresis (DG-DGGE) method consisted of PCR amplification of the target genomic DNA with GC-clamped oligonucleotides. The sequence encoded the 5′ untranslated flanking region of ferritin L-chain mRNA, which includes an IRE stem-loop structure. The product was subjected to DG-DGGE (8.5–15% polyacrylamide and 50–95% denaturant) to separate the homo- and heteroduplexes.

Results: The method clearly identified all eight accessible mutations, including C-G transversions, which are the most difficult to detect. The method was applied to scan DNA samples from 50 healthy subjects and from 230 subjects with serum ferritin &gt;400 μg/L. The new mutation G14C was identified.

Conclusions: The DG-DGGE method detects all the mutations in the L-ferritin IRE sequence, is rapid and economical, and can be applied to scan large populations. The first population study indicated that the mutations are rare and may involve regions of the IRE structure not yet characterized.

Double-gradient denaturing gradient gel electrophoresis assay for identification of L-ferritin iron-responsive element mutations responsible for hereditary hyperferritinemia-cataract syndrome: identification of the new mutation C14G

BACKGROUND

Hereditary hyperferritinemia-cataract syndrome is an autosomic dominant disorder caused by heterogeneous mutations on the iron-responsive element (IRE) of ferritin L-chain mRNA. The mutations described to date were identified by direct sequencing of DNA from probands with hyperferritinemia often associated to bilateral cataracts. A direct genetic approach on a large population is useful to recognize polymorphisms in the DNA region and the prevalence of mutations associated with minor increases in serum ferritin and subclinical cataracts. We developed a rapid DNA scanning technique to detect mutations in a single electrophoretic analysis.

METHODS

The double-gradient denaturing gradient gel electrophoresis (DG-DGGE) method consisted of PCR amplification of the target genomic DNA with GC-clamped oligonucleotides. The sequence encoded the 5' untranslated flanking region of ferritin L-chain mRNA, which includes an IRE stem-loop structure. The product was subjected to DG-DGGE (8.5-15% polyacrylamide and 50-95% denaturant) to separate the homo- and heteroduplexes.

RESULTS

The method clearly identified all eight accessible mutations, including C-G transversions, which are the most difficult to detect. The method was applied to scan DNA samples from 50 healthy subjects and from 230 subjects with serum ferritin >400 microg/L. The new mutation G14C was identified.

CONCLUSIONS

The DG-DGGE method detects all the mutations in the L-ferritin IRE sequence, is rapid and economical, and can be applied to scan large populations. The first population study indicated that the mutations are rare and may involve regions of the IRE structure not yet characterized.

Green fluorescent protein and epitope tag fusion vectors for Dictyostelium discoideum

We have constructed expression vectors for Dictyostelium discoideum which encode a green fluorescent protein (GFP) sequence upstream of a multicloning site for introduction of sequences of interest. Insertion of cDNAs into the multicloning site results in expression of fusion protein bearing an amino- or carboxyl-terminal GFP tag which can be used for fluorescent localization studies in Dictyostelium cells. A parallel construct fuses a FLAG epitope tag at the amino terminus of expressed protein. Each fusion cartridge was placed either in a G418-resistance vector allowing transactivated Ddp2-based extrachromosomal replication or in a vector allowing autonomous Ddp1-based replication. Distinct differences in expression stability were observed in the two vector types. When GFP-expressing cells were analyzed by fluorescence microscopy, significant cell-to-cell variability in expression level was observed when expression was based on the Ddp2 vector, while less cell-to-cell variation in expression level was observed when the Ddp1 backbone was used for expression.

Patients' attitudes towards the use of gloves by healthcare staff

There is a concern among healthcare providers regarding the use of gloves in non-mandated clinical situations and its impact on patient sensitivities. A convenience sample of 76 Israeli hospital inpatients were surveyed to measure patients' attitudes towards the use of gloves by healthcare providers. The Patient Sensitivity Questionnaire (PSQ) was developed and used to collect the data. Overall, patients were found to have a positive attitude towards the use of gloves in most patient care situations. Significant differences in patient attitudes towards glove use were found based on country of origin and number of hospital admissions in the previous year. The study concluded that hospitalized patients, in general, support healthcare providers' use of gloves. In addition, subjects agreed with the (American) Occupational Safety and Health Administration regulations regarding glove use.

Relationship between TNF-alpha and iron metabolism in differentiating human monocytic THP-1 cells

The human monocytic cell line THP-1 differentiates along the macrophage line after phorbol-12-myristate-13-acetate (PMA) supplementation and can be stimulated to secrete tumour necrosis factor alpha (TNF-alpha) by interferon gamma (IFN-gamma) addition. We found that, in the early stage of differentiation (1-48 h), PMA induction elicited an upregulation of intracellular H ferritin and H ferritin binding sites and a downregulation of transferrin receptor. In addition, we found that iron administration to PMA-differentiating cells induced the expression of TNF-alpha mRNA and TNF-alpha secretion to levels even higher than those induced by IFN-gamma alone. The iron chelator desferrioxamine showed the opposite effect and reduced TNF-alpha release. In contrast, preincubation of the cells with iron before PMA induction resulted in a decrease of the TNF-alpha secretion induced by IFN-gamma, whereas the opposite was true after preincubation with desferrioxamine. The data support a co-ordinate interaction between iron and TNF-alpha in monocyte macrophages, with an iron-mediated upregulation of TNF-alpha in the early phase of differentiation and an iron-mediated inhibition at later stages. This complex relationship has to be considered in evaluating the effects of iron on inflammation.

Overexpression of wild type and mutated human ferritin H-chain in HeLa cells: in vivo role of ferritin ferroxidase activity

Transfectant HeLa cells were generated that expressed human ferritin H-chain wild type and an H-chain mutant with inactivated ferroxidase activity under the control of the tetracycline-responsive promoter (Tet-off). The clones accumulated exogenous ferritins up to levels 14-16-fold over background, half of which were as H-chain homopolymers. This had no evident effect in the mutant ferritin clone, whereas it induced an iron-deficient phenotype in the H-ferritin wild type clone, manifested by approximately 5-fold increase of IRPs activity, approximately 2.5-fold increase of transferrin receptor, approximately 1.8-fold increase in iron-transferrin iron uptake, and approximately 50% reduction of labile iron pool. Overexpression of the H-ferritin, but not of the mutant ferritin, strongly reduced cell growth and increased resistance to H(2)O(2) toxicity, effects that were reverted by prolonged incubation in iron-supplemented medium. The results show that in HeLa cells H-ferritin regulates the metabolic iron pool with a mechanism dependent on the functionality of the ferroxidase centers, and this affects, in opposite directions, cellular growth and resistance to oxidative damage. This, and the finding that also in vivo H-chain homopolymers are much less efficient than the H/L heteropolymers in taking up iron, indicate that functional activity of H-ferritin in HeLa cells is that predicted from the in vitro data.

Functional and immunological analysis of recombinant mouse H- and L-ferritins from Escherichia coli

The production and characterization of recombinant mouse H- and L-ferritin chains from Escherichia coli are described. The proteins were efficiently expressed and purified with yields of 7-40 mg per liter of cell culture. They had the expected molecular mass and showed a physical stability analogous to that of the corresponding human ferritins. Mouse H- and L-ferritins had a very similar mobility on denaturing SDS-PAGE, but could be readily separated on nondenaturing PAGE because of the distinct slow mobility of mouse L-ferritin. Direct comparative experiments showed that mouse and human H-ferritins had the same iron incorporation activity, whereas mouse L-ferritin incorporated iron less efficiently than human L-ferritin. The difference was attributed to the substitution of a residue exposed on the cavity surface (Glu140 --> Lys) in mouse L-ferritin, a hypothesis confirmed by the finding that the mouse L-ferritin mutant Lys140-Glu incorporated iron as efficiently as human L-ferritin. Rabbit antisera elicited by the recombinant mouse ferritins were specific for the H- and L-chains and did not cross-react with the human ferritins. The antibodies and the derived specific ELISA assays allow the determination of H- and L-ferritins in mouse tissues.