The iron-binding properties of hen ovotransferrin

PC2 Ovotransferrin: Characterization and Alternative Immunotherapeutic Activity

Characterization and evaluation of immunotherapeutic potential of ovotransferrin PC2 (OTf PC2) were performed in this study. The ovoprotein was obtained from egg white from hens immunized with bacterial antigens, pathogenic for humans. For the negative control samples, OTf was extracted from eggs collected from Specific Pathogen-Free (SPF) hens and purified by affinity chromatography on Protein G-agarose column with two eluting peaks: I, representing ovalbumin, and II, ovotransferrin. The final apo-OTf form was reached by successive precipitation with ammonium sulfate and citric acid and the holo-OTf form by saturating the apo-form with FeCl3. Multiple OTf PC2 samples were analyzed through Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE) and, based on the molecular marker migration model, the ovotransferrin (76.5 kDa) and ovalbumin (45 kDa) were detected. The agglutination reaction exhibited statistically significant high specificity of the multiple OTf PC2, by reacting with the antigens used for hens' immunization. Following ELISA, it was established that OTf PC2 from hyperimmune eggs has specificity for all antigens; the antibody titer was high, indicating that OTf PC2 possesses immunological properties similar to immunoglobulin Y (Ig Y). This study suggests that OTf PC2 immunological activity may play a crucial role in the prevention and treatment of infections resistant to antibiotics and OTf PC2 can also act as a valuable nutraceutical.

Antimicrobial effects of novel peptides cOT2 and sOT2 derived from Crocodylus siamensis and Pelodiscus sinensis ovotransferrins

In light of the increasing threat of bacterial drug resistance to human health on a global scale, research and development of antimicrobial peptides as a novel class of potent antibiotics has gained considerable attention. The present study focuses on the structural evaluation and membrane interaction of two new cationic antimicrobial peptides, cOT2 and sOT2, derived from Siamese crocodile (Crocodylus siamensis) and Chinese softshell turtle (Pelodiscus sinensis) ovotransferrins. Here, cOT1 (+3) and sOT1 (+3) were derived from reptile ovotransferrins by chromatographic purification and characterized by mass spectrometry and N-terminal sequencing analysis. In order to increase the antimicrobial efficacy, two novel peptides, cOT2 (+6) and sOT2 (+5), were designed and synthesized as "naturally-engineered" by primary amino acid sequence extension of cOT1 and sOT1, respectively. These rational designs of modified peptides were assayed in term of antimicrobial activity. These peptides display strong antimicrobial activity against several bacterial strains, e.g. Vibrio cholerae, Bacillus megaterium, and Bacillus pumilus TISTR 905, with MICs of 7-16.1μM. In terms of structural conformation in mimic environments, CD spectroscopic analysis of the secondary peptides structure features revealed fairly the similarity on α-helical content with magainin II. Hence, the modes of actions have been speculated as toroidal and carpet model. Furthermore, the disruption of intact bacterial cells induced by cOT2 and sOT2 was investigated by SEM and AFM. The results provided evidence that cOT2 and sOT2 have the potential to cause different morphological changes of bacterial cells and that these effects can be enhanced by increasing the peptide concentration.

Optimization of Extraction Parameters for Enhanced Production of Ovotransferrin from Egg White for Antimicrobial Applications

Ovotransferrin is the second most abundant protein (~12-13% of the total egg protein) in egg white after ovalbumin. Ovotransferrin is a potent natural antimicrobial agent as it possesses antibacterial, antifungal, and antiviral properties and is also the major metal binding protein found in egg, which makes it an industrially important protein. Ovotransferrin was extracted from egg white using its metal (iron) binding properties. In the present study, eggs from two different sources were used (fresh local eggs from domestic household source and poultry eggs from shops) to compare the results and Response Surface Methodology was used for the experiment design and data analysis. The following extraction conditions were optimized so as to maximize the yield of ovotransferrin from egg white: ethanol % (v/v) and pH and volume (mL) of 25 mM FeCl₃/50 mL of egg white. A maximum yield of ~85 ± 2.5% was obtained near the optimum extraction conditions. The yield was calculated based on the theoretical value (934 mg) of ovotransferrin in 100 mL of 1.5x diluted egg white solution. Our results suggest that efficient downstream processing may reduce the cost of overall production process of this promising enzyme, making it a natural and cost-effective alternative to the existing chemically synthesized antimicrobial agents.

Molecular cloning, characterization and expression analysis of melanotransferrin from the sea cucumber Apostichopus japonicus

Melanotransferrin (MTf), a member of the transferrin families, plays an important role in immune response. But the research about MTf in sea cucumber is limited till now. In this study, the Melanotransferrin (Aj-MTf) gene was firstly cloned and characterized from the sea cucumber Apostichoupus japonicus by reverse transcriptase polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends. The full-length cDNA of Aj-MTf is 2,840 bp in length and contains a 2,184 bp open reading frame that encodes a polypeptide of 727 amino acids. An iron-responsive element-like structure is located at the 5'-UTR of Aj-MTf cDNA. Sequence analysis shows that the Aj-MTf contains two conserved domains, and the binding-iron (III) sites, including eight amino acid residues (D81,Y109,Y215,H283,D425,Y454,Y565 and H634) and three N-linked glycosylation sites (N121V122S123,N173A174S175 and N673S674T675). Quantitative real-time polymerase chain reaction (qRT-PCR) analyses suggested that the Aj-MTf expressions in the coelomic fluid, body cavity wall and respiratory trees were significantly changed from 4 to 24 h post lipopolysaccharide (LPS) injection. The mRNA levels of Aj-MTf in coelomic fluid was significantly up-regulated at 12 and 24 h in treatment group, and Aj-MTf shared a similar expression pattern with C-type lectin in coelomic fluid, while both genes appears to gradually increase after 4 h of LPS injection. These results indicate that the Aj-MTf plays a pivotal role in immune responses to the LPS challenge in sea cucumber, and provide new information that it is complementary to the sea cucumber immune genes and initiate new researches concerning the genetic basis of the holothurian immune response.

A proteomic analysis of the regulon of the NarP two-component regulatory system response regulator in the bovine pathogen Mannheimia haemolytica A1

Background

The response of the NarQP two-component signal transduction system regulon in response to the presence of nitrate for the bovine pathogen Mannheimia haemolytica A1 was investigated by proteomic analysis. Total proteins from a narP mutant and the parent SH1217 grown with or without NaNO₃ supplement were examined by ISO-DALT 2D electrophoresis and liquid chromatography-mass spectrometry.

Results

Seventeen proteins were differentially expressed in the parent strain SH1217 in response to the addition of NaNO₃ to the growth media. These responses were absent in the narP mutant, indicating that the altered production of these proteins is mediated by NarP_Mh. Interestingly, NarP_Mh mediated the increased production of some proteins which are not generally associated with nitrate respiration, such as the iron transporters FbpA and YfeA. The increased production of proteins such as superoxide dismutase, SodA, and GAPDH were also observed. The increased production of these iron-regulated proteins by NarP_Mh is thought to enhance the swift establishment of the nitrate respiration mechanism of M. haemolytica during pathogenesis.

Conclusion

The data suggested NarP_Mh acts as an important regulator which regulates the expression of a small set of proteins in response to nitrate availability. This may contribute to the prevalence of M. haemolytica A1 in its host during pathogenesis of BPP, through enhancing the effectiveness of nitrate respiration either directly or indirectly.

Evidence for a novel Entamoeba histolytica lectin activity that recognises carbohydrates present on ovalbumin

Entamoeba histolytica, an intestinal amoeba that causes dysentery and liver abscesses, acquires nutrients by engulfing bacteria in the colonic lumen and phagocytoses apoptotic cells during tissue invasion. In preliminary studies to identify ligands that stimulate amoebic phagocytosis, we used ovalbumin immobilized on latex particles as a potential negative control protein. Surprisingly, ovalbumin strongly stimulated E. histolytica particle uptake. Experiments using highly purified ovalbumin confirmed the specificity of this finding. The mechanism of particle uptake was actin-dependent, and the Entamoeba phagosome marker amoebapore A localised to ovalbumin-bead containing vacuoles. The most well described amoebic receptor is a Gal/GalNAc-specific lectin, but d-galactose had no effect on ovalbumin-stimulated phagocytosis. Ovalbumin has a single N-glycosylation site (Asn(292)) and is modified with oligomannose and hybrid-type oligosaccharides. We used both trifluoromethanesulfonic acid and N-glycanase to deglycosylate ovalbumin and tested the effect. Both methods substantially reduced the stimulatory effect of ovalbumin. Biotinylated ovalbumin bound the surface of fixed E. histolytica trophozoites saturably; furthermore, denatured ovalbumin and native ovalbumin both specifically inhibited ovalbumin-biotin binding, but deglycosylated ovalbumin had no effect. Collectively, these data suggest that E. histolytica has a previously unrecognised surface lectin activity that binds to carbohydrates on ovalbumin and stimulates phagocytosis.

The location of structural difference between ovotransferrin types A and B in hens

A comparison of ovotransferrin types A and B showed that in starch gel electrophoresis both types consisted of one major and one minor component. Both types have a similar amino acid composition as do the fragments from each type. Starch gel electrophoresis shows that the cause of the difference in the electrophoretic mobilities between ovotransferrin types A and B lies in the C-terminal half of the molecule. No physiological difference was found between types A and B, both types donate iron to chicken embryo red cells at equal rate.

An economic and simple purification procedure for the large-scale production of ovotransferrin from egg white

The objective of this study was to develop a simple and economical protocol for separating ovotransferrin from egg white. Egg white was separated from the yolk and diluted with the same volume of distilled water. To prevent denaturation during the separation process, ovotransferrin in 2x-diluted egg white was converted to its holo-form by adding 20 mM FeCl3.6H2O solution (0.25 to 3 mL/100 mL). The pH of egg white was adjusted to pH 7.0, 8.0, or 9.0, and NaHCO3 and NaCl were added to 50 mM and 0.15 M, respectively (final concentrations) to facilitate iron binding to ovotransferrin. The iron-bound ovotransferrin was separated from the egg white using different concentrations of ethanol (30 to 50%). Ethanol at 43% (final concentration) and pH at 9.0 were the best conditions for separating iron-bound ovotransferrin from 2x-diluted egg white solution. Almost all egg white proteins including ovalbumin were precipitated at 43% ethanol, but most of the iron-bound ovotransferrin remained in the supernatant. Holo-ovotransferrin in the 43% ethanol solution started to precipitate as the concentration of ethanol increased, but the optimal condition for precipitating ovotransferrin was when the ethanol concentration reached 59% (final). The precipitated holo-ovotransferrin was dissolved with distilled water, and AG1-X(2) ion exchange resin (at 3x iron content in ovotransferrin) was used to remove iron bound to ovotransferrin after pH adjustment to 4.7 using 500 mM citric acid. The apo-ovotransferrin obtained using this protocol was >80% in purity and around 99% in yield. The protocol developed is simple, economical, and appropriate for a large-scale production of ovotransferrin from egg white. Also, the isolated ovotransferrin can be applied in human foods, because the only solvent used in this process is ethanol. Furthermore, the AG1-X2 ion exchange resin and ethanol used in this process can be regenerated and recovered.

The crystal structure of iron-free human serum transferrin provides insight into inter-lobe communication and receptor binding

Serum transferrin reversibly binds iron in each of two lobes and delivers it to cells by a receptor-mediated, pH-dependent process. The binding and release of iron result in a large conformational change in which two subdomains in each lobe close or open with a rigid twisting motion around a hinge. We report the structure of human serum transferrin (hTF) lacking iron (apo-hTF), which was independently determined by two methods: 1) the crystal structure of recombinant non-glycosylated apo-hTF was solved at 2.7-A resolution using a multiple wavelength anomalous dispersion phasing strategy, by substituting the nine methionines in hTF with selenomethionine and 2) the structure of glycosylated apo-hTF (isolated from serum) was determined to a resolution of 2.7A by molecular replacement using the human apo-N-lobe and the rabbit holo-C1-subdomain as search models. These two crystal structures are essentially identical. They represent the first published model for full-length human transferrin and reveal that, in contrast to family members (human lactoferrin and hen ovotransferrin), both lobes are almost equally open: 59.4 degrees and 49.5 degrees rotations are required to open the N- and C-lobes, respectively (compared with closed pig TF). Availability of this structure is critical to a complete understanding of the metal binding properties of each lobe of hTF; the apo-hTF structure suggests that differences in the hinge regions of the N- and C-lobes may influence the rates of iron binding and release. In addition, we evaluate potential interactions between apo-hTF and the human transferrin receptor.

Sodium ferric gluconate causes oxidative stress but not acute renal injury in patients with chronic kidney disease: a pilot study

BACKGROUND

Intravenous (i.v) iron is widely used to treat anaemia in patients with chronic kidney disease (CKD). Although beneficial and usually well tolerated, concerns have been raised about its ability to cause oxidative stress and renal injury.

METHODS

To determine if i.v. iron causes oxidative stress [as assessed by plasma and urine malondialdehye (MDA)] and/or renal injury (as assessed by urinary albumin, total protein and enzymuria), we conducted a prospective, four-way randomized crossover, blinded end-point trial in eight patients with CKD. Two widely used doses of sodium ferric gluconate (125 mg infused over 1 h and 250 mg infused over 2 h) were given with or without the antioxidant N-acetylcysteine (NAC), resulting in four treatment dose-antioxidant/placebo combinations in each patient. Transferrin saturation was measured with urea polyacrylamide gel electrophoresis, MDA by high performance liquid chromatography, and albuminuria and proteinuria by standard clinical methods. Enzymuria was assessed by measurement of N-acetyl-beta-D-glucosaminidase (NAG) excretion by colorimetric assay.

RESULTS

I.v. ferric gluconate infusion at both doses resulted in a marked increase in transferrin saturation and a significant increase in plasma MDA levels. Urinary MDA levels also increased at the higher dose of iron. There was no evidence of acute renal injury, as assessed by albuminuria, proteinuria or enzymuria. Pre-treatment with NAC had no effect on oxidative stress or the above urinary parameters.

CONCLUSIONS

I.v. ferric gluconate caused oxidative stress (as reflected by increased MDA), but this was not associated with biochemical manifestations of acute renal injury.

Oxidative stress and renal injury with intravenous iron in patients with chronic kidney disease

BACKGROUND

Intravenous iron is widely prescribed in patients with chronic kidney disease (CKD) and can cause oxidative stress. The relationship of oxidative stress and renal injury in patients with CKD is unknown. Whether renal injury can occur at a time point when transferrin is incompletely saturated is also unclear.

METHODS

We conducted a randomized, open-label, parallel group trial to compare the oxidative stress induced by intravenous administration of 100 mg iron sucrose over 5 minutes and its protection with N-acetylcysteine (NAC) in 20 subjects with stage 3 or 4 CKD. Transferrin saturation was measured with urea polyacrylamide gel electrophoresis, oxidative stress by malondialdehyde (MDA) measurement by high-performance liquid chromatography, and renal injury by enzymuria and proteinuria. Reduced and oxidized glutathione and free radical scavengers as well as urinary monocyte chemoattractant protein-1 were also measured.

RESULTS

Parenteral iron increased plasma concentration and urinary excretion rate of MDA, a biomarker of lipid peroxidation, within 15 to 30 minutes of iron sucrose administration. This was accompanied by enzymuria and increase in proteinuria. In contrast, saturation of transferrin was not maximally seen until 3 hours after the end of infusion. Oxidative stress, enzymuria and proteinuria were transient and were completely resolved in 24 hours. NAC reduced acute generation of systemic oxidative stress but failed to abrogate proteinuria or enzymuria.

CONCLUSION

Intravenous iron produces oxidative stress that is associated with transient proteinuria and tubular damage. The rapid production of oxidative stress even when transferrin is not completely saturation suggests free iron independent mechanism(s) to be operative in producing oxidative stress and transient renal injury. Long-term implications of these findings need further study.

Separation of human serum transferrins with different iron-binding states by high-performance liquid chromatography using a pyridinium polymer column

Four molecular forms of transferrins with different iron-binding states were separated by HPLC using a pyridinium polymer column. The elution order was monoferric transferrin bound to the C-site, holotransferrin, apotransferrin and monoferric transferrin bound to the N-site. Human sera were also analyzed with the column, and ICP-MS combined with HPLC was used to detect iron in each peak. Transferrin peaks separated by HPLC were also confirmed by an immunological method. The percentages of iron saturation in transferrins obtained by the HPLC method were compared with the values calculated from clinical data.

Dependence of Staphylococcus epidermidis on non-transferrin-bound iron for growth

The ability of Staphylococcus epidermidis strains to grow in the presence of human transferrin and varying amounts of ferric iron was studied. At initial bacterial densities up to 10(4) cfu ml(-1), none of the three strains grew when transferrin iron saturation was below the full saturation point, whereas the bacteria grew consistently when transferrin was fully iron-saturated and there was non-transferrin-bound iron in the medium. Precultivation of the bacteria under iron-restricted conditions to induce siderophore production did not abolish the growth dependence on non-transferrin-bound iron. At initial bacterial densities of 10(6) cfu ml(-1), the bacteria proliferated consistently also in the presence of partially saturated transferrin. The results indicate that at low bacterial densities, S. epidermidis cannot utilise transferrin-bound iron for growth and that its proliferation is dependent on non-transferrin-bound iron.

Development of a pharmaceutical apotransferrin product for iron binding therapy

High-dose chemotherapy of patients with haematological malignancies results in extracellular iron accumulation and appearance of non-transferrin-bound iron, which is thought to predispose the patients to septic infections and contribute to organ toxicity. We describe the development of a human plasma-derived apotransferrin product for iron binding therapy. The product is purified from Cohn fraction IV of human plasma by two ion exchange chromatography steps and ultrafiltration. The process comprises solvent detergent treatment as the main virus inactivation step and 15 nm virus filtration and polyethylene glycol precipitation as removal steps for physico-chemically resistant infectious agents. Product characterization by electrospray and MALDI-TOF mass spectrometry indicated no other chemical modifications than N-linked glycan chains and disulphide bonds, except minor oxidation. The purity of the product was more than 98%, main impurities being IgG, IgA and hemopexin. The product had intact iron binding capacity and native conformation. A stable liquid formulation for the finished product was developed. The product has proved safe and well tolerated in early clinical trials in iron binding therapy.

Catalytically active iron and bacterial growth in serum of haemodialysis patients after i.v. iron-saccharate administration

BACKGROUND

I.v. iron is commonly administered to haemodialysis patients suffering from anaemia to improve their response to erythropoietin therapy. It has been unclear whether routinely used doses of i.v. iron preparations could result in iron release into plasma in amounts exceeding the iron binding capacity of transferrin. Here, we have studied the effect of 100 mg of iron saccharate given as an i.v. injection on transferrin saturation and the appearance of potentially harmful catalytically active iron.

METHODS

We followed serum iron, transferrin and transferrin-saturation before and 5-210 min after administration of iron saccharate in 12 patients on chronic haemodialysis due to end-stage renal disease. We measured catalytically active iron by the bleomycin-detectable iron (BDI) assay and transferrin iron forms by urea gel electrophoresis, and studied iron-dependent growth of Staphylococcus epidermidis inoculated into the serum samples in vitro.

RESULTS

The iron saccharate injection resulted in full transferrin saturation and appearance of BDI in the serum in seven out of the 12 patients. BDI appeared more often in patients with a low serum transferrin concentration, but it was not possible to identify patients at risk based on serum transferrin or ferritin level before i.v. iron. The average transferrin saturation and BDI level increased until the end of the follow-up time of 3.5 h. The appearance of BDI resulted in loss of the ability of patient serum to resist the growth of S. epidermidis, which was restored by adding iron-free apotransferrin to the serum. Iron saccharate, added to serum in vitro, released only little iron and promoted only slow bacterial growth, but caused falsely high transferrin saturation by one routinely used serum iron assay.

CONCLUSIONS

The results indicate that 100 mg of iron saccharate often leads to transferrin oversaturation and the presence of catalytically active iron within 3.5 h after i.v. injection. As catalytically active iron is potentially toxic and may promote bacterial growth, it may be recommendable to use dosage regimens for i.v. iron that would not cause transferrin oversaturation.

Differed preferential iron-binding lobe in human transferrin depending on the presence of bicarbonate detected by HPLC/high-resolution inductively coupled plasma mass spectrometry

The binding of iron (Fe) to human serum transferrin (Tf) was analyzed with an HPLC system equipped with an anion exchange column and directly connected with a high-resolution inductively coupled plasma mass spectrometer for metal detection. The (56)Fe level in the eluate was monitored at resolution m/Deltam=3000. Two monoferric Tfs were assigned based on the results of urea-PAGE and desferrioxamine experiments. When Fe was added as Fe-citrate stepwise to an apo-Tf solution in the presence of bicarbonate, the N-lobe site was the preferential Fe-binding site, while the C-lobe site was preferred in the absence of bicarbonate. In both cases, the Fe-peak areas of the preferential site and Fe(2)-Tf increased up to an Fe/Tf molar ratio of 1, and then the peak area of the monoferric Tf decreased while the peak area of Fe(2)-Tf increased. When the Fe/Tf molar ratio was below 1, the amount of Fe bound to the lobe with a weaker affinity was higher in Fe(2)-Tf than in the monoferric Tf in each case. Namely, Fe(2)-Tf was the preferential binding state of Fe to human serum Tf. The preference is reasonable for transferring Fe ions effectively to Tf-receptors.

Crystal structure of hen apo-ovotransferrin. Both lobes adopt an open conformation upon loss of iron

The three-dimensional crystal structure of hen apo-ovotransferrin has been solved by molecular replacement and refined by simulated annealing and restrained least squares to a 3.0-A resolution. The final model, which comprises 5312 protein atoms (residues 1 to 686) and 28 carbohydrate atoms (from two monosaccharides attached to Asn(473)), gives an R-factor of 0.231 for the 11,989 observed reflections between 20.0- and 3.0-A resolution. In the structure, both empty iron binding clefts are in the open conformation, lending weight to the theory that Fe(3+) binding or release in transferrin proceeds via a mechanism that involves domain opening and closure. Upon opening, the domains rotate essentially as rigid bodies. The two domains of the N-lobe rotate away from one another by 53 degrees, whereas the C-lobe domains rotate away each another by 35 degrees. These rotations take place about an axis that passes through the two beta-strands, linking the domains. The domains of each lobe make different contacts with one another in the open and closed forms. These contacts form two interdomain interfaces on either side of the rotation axis, and domain opening or closing produces a see-saw motion between these two alternative close-packed interfaces. The interdomain disulfide bridge (Cys(478)-Cys(671)), found only in the C-lobe, may restrict domain opening but does not completely prevent it.

Evidence for the glycosylation of porcine serum transferrin at a single site located within the C-terminal lobe

In this study we report the number and location of the glycans on PST. Urea PAGE and SDS-PAGE have been used to follow the enzymatic removal of sialic acids and of glycans from PST and the masses of native and deglycosylated PST have been determined by electrospray mass spectrometry. The results are consistent with the presence of a single biantennary glycan chain. As amino acid sequence analysis demonstrated the absence of a glycosylated asparagine at position 25, the glycosylation site is restricted to Asp-497.

Calorimetric studies of serum transferrin and ovotransferrin. Estimates of domain interactions, and study of the kinetic complexities of ferric ion binding

Human serum transferrin and hen ovotransferrin have been studied by differential scanning calorimetry (DSC), in an effort to quantitatively estimate the free energy of interaction of the N- and C-domains in each protein and to further understand their interaction with chelated ferric ions. In the case of serum transferrin, separate DSC transitions are observed for the two domains while only a single, coupled transition is seen for ovotransferrin. Although domain interactions are somewhat larger for ovotransferrin (-4100 cal/mol) than for serum transferrin (-3100 cal/mol), the major cause of separated transitions for serum transferrin is that the difference in intrinsic folding stability of the N- and C-domains is about 4-fold larger than for ovotransferrin. Chelated ferric ions bind strongly to each site in both proteins and produce changes in Tm by as much as 30 degrees C. When apparent binding constants are estimated from DSC results, these appear to be substantially larger than those estimated previously from equilibrium methods at low temperatures, where very long equilibrium times must be used because of slow ligand release. Although second DSC upscans on each protein show good "reversibility", downscans on serum transferrin revealed that liganded forms of the protein are in fact not in true equilibrium during upscanning, which causes Tm values during upscans to be higher than the true reversible Tm values. The likely reason for this kinetic control over unfolding is the slow release of bound ferric ions and those effects, for technical reasons, cannot be totally eliminated by lowering the scan rate.

Evidence for a single glycan moiety in rabbit serum transferrin and location of the glycan within the polypeptide chain

The sequential removal of N-acetylneuraminic acid from rabbit serum transferrin has been followed by urea-polyacrylamide gel electrophoresis. The electrophoretic pattern is consistent with the presence of a single biantennary glycan chain. From the amino acid sequence of the carbohydrate-containing cyanogen bromide fragment we have shown that the glycan is attached to an asparaginyl side chain at a position equivalent to residue 491 in the sequence of human serum transferrin.

Kinetics of pyrophosphate induced iron release from diferric ovotransferrin

The kinetics of pyrophosphate-induced iron release from diferric ovotransferrin were studied spectrophotometrically at 37 degrees C in 0.1 M HEPES, pH 7.0. At high pyrophosphate concentrations, the kinetics are biphasic, indicating that the rates of iron release from the two, presumably noninteracting iron-binding sites of ovotransferrin are different. The pseudo-first-order rate constants for iron release from both the fast and slow sites exhibit a hyperbolic dependence on pyrophosphate concentrations. The data suggest that pyrophosphate forms complexes with the two iron-binding sites of ovotransferrin prior to iron removal. The stability constants of the complex formed with the fast site (Keqf) and slow site (Keqs) are 8.3 M-1 and 40.4 M-1, respectively. The first-order rate constants for the dissociation of ferric-pyrophosphate from the fast site (k2f) and the slow site (k2s) are 0.062 and 0.0044 min-1, respectively. Results from urea gel electrophoresis studies suggest that iron is released at a much faster rate from the N-terminal binding site of ovotransferrin. At high pyrophosphate concentration, only C-monoferric-ovotransferrin is detected during the course of iron release. At low pyrophosphate concentration, however, a detectable amount of N-monoferric-ovotransferrin is accumulated. This result is consistent with the kinetic finding that the site with a higher k2 (0.062 min-1) has a lower affinity toward pyrophosphate (Keq = 8.3 M-1) whereas the site with a lower k2 (0.0044 min-1) has a higher affinity for pyrophosphate (Keq = 40.4 M-1).

Copper complexes at N- and C-site of ovotransferrin: quantitative determination and visible absorption spectrum of each complex

Copper complexes at the two sites of ovotransferrin (TF) differed markedly in the rate of Cu release by EDTA. During the reaction, lambda max of the remaining Cu-Tf complex shifted to red side, while the difference spectrum of FenCu2-nTf vs. FenTf in which the N-site had been preferentially occupied with Fe had lambda max at blue side from that of Cu2Tf, 440 nm. From these results, the intrinsic spectrum for Cu-complex at each site was assigned: lambda max 450 nm for N- and 430 nm for C-site. The differences in the release rate and the spectrum can be used for the identification of the two domains of Tf and for the analysis of metal-binding behavior of each site.

The complete nucleotide sequence of the chicken ovotransferrin mRNA

The nucleotide sequence of an almost double-stranded cDNA copy [Cochet, M., Perrin, F., Gannon, F., Krust, A., Chambon, P., McKnight, G. S., Lee, D. C., Mayo, K. E., and Palmiter, R. D. (1979) Nucleic Acids Res. 6, 2435-2452] of chicken ovotransferrin (conalbumin) mRNA has been determined. Taking into account the previously reported 5'-end sequence [Cochet, M., Gannon, F., Hen, R., Maroteaux, L., Perrin, F., and Chambon, P. (1979) Nature (Lond.) 282, 567-574] we present the complete nucleotide sequence of the ovotransferrin mRNA from which the amino acid sequence of the protein is inferred. A computer and statistical analysis of the nucleotide sequence reveals a pattern of internal homology which confirms that the present-day chicken ovotransferrin gene (and by extrapolation the transferrin genes of other species) has evolved by duplication and gives some support to the quadruplication hypothesis of transferrin evolution.

The distribution of iron between the metal-binding sites of transferrin human serum

The Makey & Seal [(1976) Biochim. Biophys. Acta 453, 250--256] method of polyacrylamide-gel electrophoresis in buffer containing 6 M-urea was used to determine the distribution of iron between the N-terminal and C-terminal iron-binding sites of transferrin in human serum. In fresh serum the two sites are unequally occupied; there is preferential occupation of the N-terminal site. On incubation of the serum at 37 degrees C the preference of iron for the N-terminal site becomes more marked. On storage of serum at -15 degrees C the iron distribution changes so that there is a marked preference for the C-terminal site. Dialysis of serum against buffer at pH 7.4 also causes iron to be bound much more strongly by the C-terminal than by the N-terminal site. The original preference for the N-terminal site can be resroted to the dialysed serum by addition of the diffusible fraction.