Ferroxidase Activity Research Articles

Ceruloplasmin enhances DNA damage induced by cysteine/iron in vitro

Ceruloplasmin (Cp) was found to promote the oxidative damage to DNA in vitro, as evidenced by the formation of 8-hydroxy-2’-deoxyguanosine and strand breaks, when incubated with a cysteine metal-catalyzed oxidation system (Cys-MCO) comprised of Fe 3+, O 2, and cysteine as an electron donor. The capacity of Cp to enhance oxidative damage to DNA was inhibited by hydroxyl radical scavengers such as sodium azide and mannitol, a metal chelator, diethylenetriaminepentaacetic acid, a spin-trapping agent, 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and catalase. Ceruloplasmin also caused the two-fold enhancement of a mutation in the pUC18 lacZ’ gene in the presence of Cys-MCO when measured as a loss of α-complementation. Incubation of Cp with Cys-MCO resulted in an increase in the content of carbonyl groups and the significant alteration of the ferroxidase activity, as well as the proteolytic susceptibility. The deoxyribose assay and the salicylate hydroxylation assay showed that hydroxyl free radicals were generated in the reaction of Cp with Cys-MCO. The release of a portion of Cu from Cp was observed, and conformational alterations were indicated by the changes in fluorescence spectra. Based on these results, we interpret the enhancing effect of Cp on DNA damage and mutagenicity induced by Cys-MCO as due to reactive oxygen species, probably hydroxyl free radicals, formed by the reaction of free Cu 2+, released from oxidatively damaged Cp, and H 2O 2 produced by Cys-MCO. The release of Cu from Cp during oxidative stress could enhance the formation of reactive oxygen species and could also potentiate cellular damage.

"Opening" the ferritin pore for iron release by mutation of conserved amino acids at interhelix and loop sites.

Ferritin concentrates, stores, and detoxifies iron in most organisms. The iron is a solid, ferric oxide mineral (< or =4500 Fe) inside the protein shell. Eight pores are formed by subunit trimers of the 24 subunit protein. A role for the protein in controlling reduction and dissolution of the iron mineral was suggested in preliminary experiments [Takagi et al. (1998) J. Biol. Chem. 273, 18685-18688] with a proline/leucine substitution near the pore. Localized pore disorder in frog L134P crystals coincided with enhanced iron exit, triggered by reduction. In this report, nine additional substitutions of conserved amino acids near L134 were studied for effects on iron release. Alterations of a conserved hydrophobic pair, a conserved ion pair, and a loop at the ferritin pores all increased iron exit (3-30-fold). Protein assembly was unchanged, except for a slight decrease in volume (measured by gel filtration); ferroxidase activity was still in the millisecond range, but a small decrease indicates slight alteration of the channel from the pore to the oxidation site. The sensitivity of reductive iron exit rates to changes in conserved residues near the ferritin pores, associated with localized unfolding, suggests that the structure around the ferritin pores is a target for regulated protein unfolding and iron release.

Blood transfusion increases radical promoting non-transferrin bound iron in preterm infants

BACKGROUNDBlood transfusion has been recognised as a risk factor for the development of retinopathy of prematurity (ROP) or chronic lung disease (CLD) in preterm infants, but the precise mechanism involved...

Results of genetic testing: when confidentiality conflicts with the duty to warn relatives

When a patient is found to have an inherited disease, it has implications for the whole family. If screening is available, the test is usually offered to all relatives who could be affected, but what if the patient does not want to tell his or her family about this diagnosis? As his general practitioner, you referred Andrew, a 23-year-old man, to the local psychiatrist because of gradual onset of paranoid ideation. From the hospital correspondence, you gather that the psychiatrist detected dysarthria and abnormal involuntary movements and asked for a neurologist's opinion. The neurologist diagnosed Wilson's disease (hepatolenticular degeneration), and Andrew began chelation therapy under the care of a specialist. You know Andrew's background reasonably well because you are the general practitioner for his 21-year-old brother, Martin, and his 20-year-old sister, Alison. Their father died many years ago in a traffic accident, and their mother died of breast cancer 2 years ago. Andrew lived with Martin and Alison until last year when he moved out to live with his girlfriend, in part because of his increasing mistrust of Martin and Alison. Because the inheritance of Wilson's disease is autosomal recessive, both Martin and Alison have a 1-in-4 risk of having the disease. The disease is treatable in the presymptomatic stage, and you are anxious to ensure that Martin and Alison receive appropriate counseling and testing. You learn from Andrew, however, that Martin and Alison have not received such counseling. Indeed, when the staff at the specialty clinic asked Andrew whether he had any siblings, he replied that he had none. Although you explain to Andrew the importance of Martin and Alison receiving early counseling and testing, Andrew is clear that he does not want anyone to inform them about his diagnosis. He seems to understand the potential consequences of his refusal to inform Martin and Alison. Under these circumstances, you have 3 options: to inform Martin and Alison about Andrew's recent diagnosis and refer them for appropriate counseling and testing; to take a blood specimen from Martin and Alison to test the serum ferroxidase activity (a screening test for Wilson's disease) without informing them of the reason; or to take no action.

Proton and metal ion-dependent assembly of a model diiron protein.

DF1 is a small, idealized model for carboxylate-bridged diiron proteins. This protein was designed to form a dimeric four-helix bundle with a dimetal ion-binding site near the center of the structure, and its crystal structure has confirmed that it adopts the intended conformation. However, the protein showed limited solubility in aqueous buffer, and access to its active site was blocked by two hydrophobic side chains. The sequence of DF1 has now been modified to provide a very soluble protein (DF2) that binds metal ions in a rapid and reversible manner. Furthermore, the DF2 protein shows significant ferroxidase activity, suggesting that its dimetal center is accessible to oxygen. The affinity of DF2 for various first-row divalent cations deviates from the Irving-Willliams series, suggesting that its structure imparts significant geometric preferences on the metal ion-binding site. Furthermore, in the absence of metal ions, the protein folds into a dimer with concomitant binding of two protons. The uptake of two protons is expected if the structure of the apo-protein is similar to that of the crystal structure of dizinc DF1. Thus, this result suggests that the active site of DF2 is retained in the absence of metal ions.

High levels of ceruloplasmin in the serum of transgenic mice developing hepatocellular carcinoma

Transgenic mice expressing the Simian virus 40 large T antigen under the control of the liver-specific human antithrombin-III promoter all develop well-differentiated hepatocellular carcinoma. During tumour development serum ceruloplasmin (Cp) increases gradually until it reaches 30 times control levels in all transgenic mice at 6 months of age. The accumulation of Cp in the serum is due to the increased transcription of the Cp gene as well as to the increase in Cp mRNA stability in the livers of the transgenic mice. One-half of the overproduced Cp is charged with copper and Cp-associated serum oxidase activity increases in parallel with the holo-Cp concentration. Through its ferroxidase activity Cp is involved prominently in iron metabolism. Analysis of copper and iron in serum and liver revealed increased copper levels in the serum of tumour-bearing animals and which increased in parallel with Cp concentration; the amounts of copper in the liver were unchanged. In contrast, serum iron remained constant during tumour development whereas the iron concentration in the livers of the transgenic mice decreased.

Ferroxidases and xanthine oxidase in plasma of healthy newborn infants

In the neonatal period, there is a high iron load, while both the level and molar oxidase activity of ceruloplasmin are low. On the other hand, the neonatal xanthine oxidase (XO) activity is higher than later in life and XO has a significant iron-oxidizing capacity. We therefore studied the physiological contribution of XO to the ferroxidase activity of the plasma in 20 full-term newborn infants. Ferroxidase activity was measured spectrophotometrically, with Fe++ as substrate. The uric acid formed by XO was assayed by means of HPLC, with electrochemical detection.The total ferroxidase activity in the plasma was about one-fourth of the adult level and rapidly increased doubling within 3 days after birth. About 90% of the plasma ferroxidase activity was due to ceruloplasmin, the remainder being accounted for by ferroxidase II. The XO activity underwent a 30% (statistically non-significant) elevation at 24 h, though ferroxidase activity attributable to XO was not detected at any time.Accordingly, XO does not seem to add substantially to the total iron-oxidizing capacity of the plasma in the neonatal period. The high molar ferroxidase activity is probably of importance at the endothelial cell surface.

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.

Site-directed Mutagenesis of Human Ceruloplasmin: PRODUCTION OF A PROTEOLYTICALLY STABLE PROTEIN AND STRUCTURE-ACTIVITY RELATIONSHIPS OF TYPE 1 SITES

A fully active recombinant human ceruloplasmin was obtained, and it was mutated to produce a ceruloplasmin stable to proteolysis. The stable ceruloplasmin was further mutated to perturb the environment of copper at the type 1 copper sites in two different domains. The wild type and the mutated ceruloplasmin were produced in the yeast Pichia pastoris and characterized. The mutations R481A, R701A, and K887A were at the proteolytic sites, did not alter the enzymatic activity, and were all necessary to protect ceruloplasmin from degradation. The mutation L329M was at the tricoordinate type 1 site of the domain 2 and was ineffective to induce modifications of the spectroscopic and catalytic properties of ceruloplasmin, supporting the hypothesis that this site is reduced and locked in a rigid frame. In contrast the mutation C1021S at the type 1 site of domain 6 substantially altered the molecular properties of the protein, leaving a small fraction endowed with oxidase activity. This result, while indicating the importance of this site in stabilizing the overall protein structure, suggests that another type 1 site is competent for dioxygen reduction. During the expression of ceruloplasmin, the yeast maintained a high level of Fet3 that was released from membranes of yeast not harboring the ceruloplasmin gene. This indicates that expression of ceruloplasmin induces a state of iron deficiency in yeast because the ferric iron produced in the medium by its ferroxidase activity is not available for the uptake.

Oxidase activity of ceruloplasmin and concentrations of copper and zinc in serum of cancer patients

A balance between oxidant carcinogens and endogenous antioxidant defence is of particular relevance to the carcinogenesis. Ceruloplasmin (Cp) carries up to 90% of Cu in plasma and performs ferroxidase, antioxidant and amine oxidase activity. Cu and Zn, as trace elements, have been recognized to play an important role as cofactors of SOD. The study presents the relationship of the Cp oxidase activity and concentrations of Cu and Zn in serum of 62 patients with breast (BCA), lung (LCA), gastrointestinal (GICA) and gynecological (GYNCA) cancer. The Cp oxidase activity was determined in serum with o-dianisidine as a substrate. Cu and Zn concentrations in serum were measured by using atomic absorption spectrometry. The results of the study have shown significant increase in the mean serum Cp oxidase activity and total Cu concentrations in all patient groups compared with the control one. The total mean serum Zn concentration was found to be decreased only in LCA group as compared with the control. The effect of the cancer progress on the Cp oxidase activity and concentrations of Cu and Zn was observed within the group of all cancer patients (ALLCA) and within the GICA group. The only significant difference in Cu concentrations among various stages of the disease was observed in GICA between local and distant one. Significant positive correlation coefficients were calculated for the Cp activity and Cu concentrations in the control group and all patients groups, also according to the cancer progress. Future research is needed to evaluate the consequences of the elevation of the serum Cp oxidase activity and concentration of Cp, Cu and Zn for the host antioxidant-oxidant balance.

Intact Human Ceruloplasmin Is Required for the Incorporation of Iron into Human Ferritin

We have previously reported several studies on the loading of iron into ferritin by ceruloplasmin using proteins from rats. Loading iron into human ferritin using human serum ceruloplasmin is complicated by the fact that human ceruloplasmin is very susceptible to proteolysis (T. P. Ryan, T. A. Grover, and S. D. Aust, 1992, Arch. Biochem. Biophys. 293, 1–8). The present study investigated the effect of proteolysis on the ability of human ceruloplasmin to load iron into human ferritin. SDS–PAGE revealed one major band with an apparent molecular weight of 116 kDa for a proteolytically degraded form of ceruloplasmin versus a 132-kDa band for an intact form of the enzyme. Both forms of the enzyme possessed ferroxidase activity, although that of the proteolytically degraded enzyme was approximately twofold less than that of the intact enzyme (4.9 nmol (min)−1 vs 8.3 nmol (min)−1). Only the intact form of ceruloplasmin was able to catalyze iron loading into ferritin without altering the physical characteristics of the ferritin protein during the process. Abnormal migration in nondenaturing PAGE gels, as well as a decrease in the amount of detectable ferritin protein, was observed when ferritin was incubated with iron alone or with proteolytically degraded ceruloplasmin and iron. It was concluded that the structural integrity of ceruloplasmin is required for the enzyme to effectively catalyze iron loading into ferritin.

Postnatal Changes in Plasma Ceruloplasmin and Transferrin Antioxidant Activities in Preterm Babies

Postnatal changes in plasma ceruloplasmin ferroxidase and transferrin iron-binding antioxidant activity were studied in 10 healthy preterm babies during the first 6 weeks of life. Ceruloplasmin levels and ceruloplasmin ferroxidase activity were low at birth, remained stable for the first 3 weeks, and increased between 3 and 6 weeks. The transferrin levels were also low at birth, and this finding persisted throughout the 6-week study period. However, although the plasma iron-binding antioxidant activity was correspondingly low at birth, it thereafter rose and remained high. In four cord blood samples, but not in subsequent postnatal samples, peroxidation was actually stimulated in the assay measuring plasma iron-binding antioxidant activity. We have previously shown that this phenomenon is probably due to the presence of non-protein-bound iron.

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.

Role of Hypoxia-inducible Factor-1 in Transcriptional Activation of Ceruloplasmin by Iron Deficiency

A role of the copper protein ceruloplasmin (Cp) in iron metabolism is suggested by its ferroxidase activity and by the tissue iron overload in hereditary Cp deficiency patients. In addition, plasma Cp increases markedly in several conditions of anemia, e.g. iron deficiency, hemorrhage, renal failure, sickle cell disease, pregnancy, and inflammation. However, little is known about the cellular and molecular mechanism(s) involved. We have reported that iron chelators increase Cp mRNA expression and protein synthesis in human hepatocarcinoma HepG2 cells. Furthermore, we have shown that the increase in Cp mRNA is due to increased rate of transcription. We here report the results of new studies designed to elucidate the molecular mechanism underlying transcriptional activation of Cp by iron deficiency. The 5'-flanking region of the Cp gene was cloned from a human genomic library. A 4774-base pair segment of the Cp promoter/enhancer driving a luciferase reporter was transfected into HepG2 or Hep3B cells. Iron deficiency or hypoxia increased luciferase activity by 5-10-fold compared with untreated cells. Examination of the sequence showed three pairs of consensus hypoxia-responsive elements (HREs). Deletion and mutation analysis showed that a single HRE was necessary and sufficient for gene activation. The involvement of hypoxia-inducible factor-1 (HIF-1) was shown by gel-shift and supershift experiments that showed HIF-1alpha and HIF-1beta binding to a radiolabeled oligonucleotide containing the Cp promoter HRE. Furthermore, iron deficiency (and hypoxia) did not activate Cp gene expression in Hepa c4 hepatoma cells deficient in HIF-1beta, as shown functionally by the inactivity of a transfected Cp promoter-luciferase construct and by the failure of HIF-1 to bind the Cp HRE in nuclear extracts from these cells. These results are consistent with in vivo findings that iron deficiency increases plasma Cp and provides a molecular mechanism that may help to understand these observations.

Plasma proteins modified by tyrosine nitration in acute respiratory distress syndrome.

The present study identifies proteins modified by nitration in the plasma of patients with ongoing acute respiratory distress syndrome (ARDS). The proteins modified by nitration in ARDS were revealed by microsequencing and specific antibody detection to be ceruloplasmin, transferrin, alpha(1)-protease inhibitor, alpha(1)-antichymotrypsin, and beta-chain fibrinogen. Exposure to nitrating agents did not deter the chymotrypsin-inhibiting activity of alpha(1)-antichymotrypsin. However, the ferroxidase activity of ceruloplasmin and the elastase-inhibiting activity of alpha(1)-protease inhibitor were reduced to 50.3 +/- 1.6 and 60.3 +/- 5.3% of control after exposure to the nitrating agent. In contrast, the rate of interaction of fibrinogen with thrombin was increased to 193.4 +/- 8.5% of the control value after exposure of fibrinogen to nitration. Ferroxidase activity of ceruloplasmin and elastase-inhibiting activity of the alpha(1)-protease inhibitor in the ARDS patients were significantly reduced (by 81 and 44%, respectively), whereas alpha(1)-antichymotrypsin activity was not significantly altered. Posttranslational modifications of plasma proteins mediated by nitrating agents may offer a biochemical explanation for the reported diminished ferroxidase activity, elevated levels of elastase, and fibrin deposits detected in patients with ongoing ARDS.

Intrinsic ferroxidase activity in the Alzheimer's amyloid precursor protein

Intrinsic ferroxidase activity in the Alzheimer's amyloid precursor protein

The essential role of Glu-185 and Tyr-354 residues in the ferroxidase activity of Saccharomyces cerevisiae Fet3

The structural determinants required for ferroxidase activity by the yeast multicopper oxidase Fet3 have been partially clarified by site-directed mutagenesis based on homology modeling. Glu-185 and Tyr-354 were substituted with Ala and Phe, respectively. Fet3 E185A retained ca. 5% residual ferroxidase catalytic efficiency, and almost 40% oxidase efficiency. On the other hand, Fet3 Y354F exhibited 50% residual efficiency as a ferroxidase and more than 70% as an oxidase. These results provide new insights in the mechanism of iron binding and oxidation by Fet3, establishing the essential role of Glu-185 and Tyr-354, and allowing to dissect ferroxidase from non-iron oxidase activity.

The Ferroxidase Activity of Caeruloplasmin Is Reduced in Haemodialysis Patients

Increased free-radical production leading to oxidative stress may contribute to the development of cardiovascular complications in haemodialysis patients. The ferroxidase activity of caeruloplasmin forms an important component of antioxidant defences in body fluids. The aim of this study was to assess ferroxidase activity in haemodialysis patients. Venous blood was collected from 83 haemodialysis patients immediately prior to and after dialysis and from 52 healthy controls. Immunoreactive caeruloplasmin was measured by rate nephelometry, and ferroxidase activity determined by measuring loading of ferrous iron onto iron-free transferrin. A significant reduction in ferroxidase activity was observed in dialysis patients when compared with controls (37 ± 1.20 and 46 ± 1.14 mU/l, respectively; p < 0.001). Following dialysis, ferroxidase activity rose significantly to 41 ± 1.16 mU/l, with a significant difference still remaining between control and patient ferroxidase activity (p < 0.005). Immunoreactive caeruloplasmin was found to be similar in all groups (before dialysis 0.40 ± 0.07 g/l, after dialysis 0.39 ± 0.07 g/l, control 0.42 ± 0.09 g/l: p = NS). A significant difference in caeruloplasmin-specific activity was therefore observed between predialysis, postdialysis and control samples (97 ± 2.31, 105 ± 1.74 and 112 ± 1.51 mU/g; p < 0.001, p < 0.01, respectively). Ferroxidase activity of caeruloplasmin is impaired in renal failure. Inhibition of caeruloplasmin ferroxidase activity in dialysis patients may contribute to increased oxidative stress in these patients.

Interaction between 6-hydroxydopamine and transferrin: "Let my iron go".

The dopamine analogue 6-hydroxydopamine (6-OHDA) is selectively toxic to catecholaminergic neurons. Because of its selectivity for neuroblastic cells in the sympathetic nervous system lineage, 6-OHDA has been suggested as a chemotherapeutic agent for targeted treatment of patients with neuroblastoma. We tested the hypothesis that the toxicity of 6-OHDA is caused by its interaction with serum ferric transferrin (Fe-TF) resulting in release of iron. We further hypothesized that this iron, through its redox-cycling by 6-OHDA, triggers generation of reactive oxygen species. 6-OHDA-induced release of iron from Fe-TF was demonstrated by: (1) low-temperature EPR spectroscopic evidence for decay of the characteristic Fe-TF signal (g = 4.3) and appearance of the high-spin signal from iron chelated by 6-OHDA oxidation products; (2) spectrophotometric detection of complexing of iron with the Fe(2+) chelator ferrozine; (3) redox-cycling of ascorbate yielding EPR-detectable ascorbate radicals; and (4) generation of hydroxyl radicals as evidenced by EPR spectroscopy of their adduct with a spin trap, 5, 5'-dimethylpyrroline oxide (DMPO) (DMPO-OH). Our low-temperature EPR studies showed that in human plasma, 6-OHDA caused iron release only under nitrogen gas but not under air or oxygen. The absence of a 6-OHDA effect in plasma under aerobic conditions was most likely due to its ferroxidase activity [with consequent reuptake of Fe(III) by apoTF] and catalytic oxidation of 6-OHDA by ceruloplasmin. Modeling of these plasma activities by a stable nitroxide radical, 2,2,6, 6-tetramethyl-1-piperidinyloxy (TEMPOL), resulted in protection of plasma Fe-TF against iron release under nitrogen. Parenteral administration of 6-OHDA to mice resulted in iron release from Fe-TF as evidenced by transformation of the Fe-TF low-temperature EPR signal that was indistinguishable from that seen in in vitro models. In addition, administration of the iron chelator deferoxamine (DFO) to mice prior to administration of toxic doses of 6-OHDA resulted in a decrease in activity impairment of mice as compared to that seen with 6-OHDA alone. These findings underscore the physiological and pharmacological relevance of 6-OHDA-mediated iron release from Fe-TF and suggest that iron chelators (DFO) may be used for prevention of 6-OHDA toxicity.

Alternative RNA Splicing Generates a Glycosylphosphatidylinositol-anchored Form of Ceruloplasmin in Mammalian Brain

Ceruloplasmin is a copper-containing ferroxidase that is essential for normal iron homeostasis. Whereas ceruloplasmin in plasma is produced and secreted by hepatocytes, in the brain a glycosylphosphatidylinositol (GPI)-anchored form of ceruloplasmin is expressed on the surface of astrocytes. By using a cDNA cloning approach, we have now determined that the GPI-anchored form of ceruloplasmin is generated by alternative RNA splicing. The splicing occurs downstream of exon 18 and replaces the C-terminal 5 amino acids of the secreted form with an alternative 30 amino acids that signal GPI anchor addition. RNase protection analysis demonstrates that the GPI-anchored form is the major form in the brain, whereas the secreted form predominates in the liver. Individuals with aceruloplasminemia, a hereditary deficiency of ceruloplasmin, have severe iron deposition in a number of organs, including the brain where it results in neurodegeneration. Therefore, this novel GPI-anchored form of ceruloplasmin is likely to play an important role in iron metabolism in the central nervous system.